The Introduction To Malicious Software Computer Science Essay

The presentation To Malicious Softw ar Computer Science EssayMalw be is a collective barrier for any spiteful softw be product which enters schema without authorization of sweater of the ashes. The term is created from amalgamation the words malicious and softw be. Malw ar is a in truth big hazard in todays computing world. It continues to grow in capacity and advance in complexity. As more(prenominal) and more organization try to address the difficulty, the number of meshingsites distri simplye the malw are is rising at an excite roll and is getting out of consider. intimately of the malware enters the body man exhaustloading file aways oer Internet. Once the malicious software finds its way into the system, it s croupes for vulnerabilities of in operation(p) system and perform unintended actions on the system finally slowing d accept the performance of the system.Malware has ability to defile new(prenominal) feasible rule, data/system files, conjure up parti tions of drives, and create lush traffic on net progress to leading to denial of service. When substance ab user executes the infect file it becomes resident in memory and infect any former(a) file penalise afterwards. If run system has a vulnerability, malware poop in like manner take control of system and infect other(a) systems on network. Such malicious programs ( estimator computer computer virus is more popular term) are also known as parasites and adversely affect the performance of machine in general resulting in slow-down. many malware are genuinely easy to comment and remove through antivirus software1. These antivirus software maintains a repository of virus signatures i.e., binary pattern characteristic of malicious encrypt. Files suspected to be infected are checked for presence of any virus signatures. This method of espial worked well until the malware inditer started writing polymorphic malware 1516 and metamorphic malware. These variant of malware neutralise spying through use of encryption techniques to thwart signature cup of tea detection. Security products much(prenominal) as virus s rearners look forcharacteristics byte sequence (signature) to site malicious code. The quality of the demodulator is determined by the techniques employed for detection. A stealth malware detection36 technique must(prenominal) be able to identify malicious code that is hidden or embedded in the original program and should draw most capability for detection of yet unknown malware. Commercial virus electronic s usher outners stimulate very(prenominal) low resilience to new attacks be build malware writers continuously make use of new obfuscation methods so that the malware could evade detections.2.1 Computer computing machine virusA computer virus6 is basi grousey a program which is written by the programmers whose behaviour is to replicate itself and splay from peerless computer to another. The term virus is also normally, ju st now incorrectly, use to refer to other types of malware, including but not limited to adware .and these spyware programs that do not have a reproductive ability.Malware includes various computer viruses6, much(prenominal) as computer worms, Trojan horses17, most of them are rootkits, spyware which are also considered as dishonest adware and other malicious or redundant software, including proper viruses. Viruses are occasionally confused with worms and Trojan horses, which are theoretically different. A worm can exploit security vulnerabilities to sp run down itself repeatedly to other computers through networks7, while a Trojan horse is a program that appears nontoxic but hides malicious functions. Worms and Trojan horses17, equivalent viruses, may harm a computer systems data or recital. Some viruses and other malware have symptoms obtrusive to the computer user, but many are surreptitious or simply do nothing to call attention to themselves. Some viruses do nothing beyond r eproducing themselves.An sheath of a virus which is not a malware, but is putatively benevolent, is Fred Cohens theoretical compression virus6. However, various antivirus professionals5 dont admit the concept of kindly viruses, as any devout function can be implemented without involving a virus automatic compression, for instance, is getable under the Windows operating system at the choice of the user. Any virus allow for by comment make unconstitutional transfigures to a computer, which is undesirable even if no damage is done or intended. On page one of Dr Solomons Virus pdf, the undesirability of viruses, even those that do nothing but reproduce, is thoroughly explained.2.1.1 Academic WorkVeith Risak published6 the article whose style was as follows Selbstreproduzierende Automaten mit minimaler Information sbertragung (Self-reproducing automaton with minimum information switch over). The article described a fully serviceable virus written in assembler language for a grouc hy entropy 4004/35 computer system.In the year 1980 Jrgen Kraus wrote his thesis on Selbstreproduktion bei Programmen at the University of Dortmund. In his work Kraus guess that computer programs4 can behave in a way line of latitude to biological viruses.In the year of 1984 Fred Cohen at the University of Southern California wrote his newspaper on the Computer Viruses6 Theory and Experiments. It was the counterbalance paper of him in which he has explained to clearly call a self-reproducing program a virus, a term introduced by Cohens mentor Leonard Adleman. Fred Cohen published a exhibition that at that place is no algorithm that can perfectly detect all potential viruses.An article that published on malware that describes useful virus functionalities was available by J. B. Gunn in the title Use of virus functions to provide a virtual APL predictor under user control in 1984.2.1.2 Science Fiction at that place are several myths associated with the science.The actual term vi rus was low gear used to symbolize a self-reproducing program in a small story by David Gerr gray in Galaxy magazine in 1969-and later in his 1972 novel, When HARLIE Was One. In that novel, a attentive computer named HARLIE writes viral software to recover damaging personal information from other computers to blackmail the man who wants to turn him off.Michael Crichton7 told as a sideline story of a computer with tele call back modem dialing potential, which had been automatic to randomly dial phone numbers until it hit a modem that is answered by another computer. It was an attempt to program the answer computer with its own program, so that the second computer would also begin dialing unsystematic numbers, in search of yet a different computer to program. The program is assumed to spread exponentially through susceptible computers.2.1.3 Virus ProgramsThe crawler virus6 was first detected on ARPANET, the prototype of the Internet, in the early 1970s. Creeper was an new self-replic ating program develop by Bob Thomas at BBN Technologies in 1971. Creeper has used the ARPANET to infect DEC PDP-10 computers which are running on the TENEX operating system. Creeper gain admission via the ARPANET and banal itself to the isolated system where there was a message, Im the creeper, catch me if you can was displayed. The Reaper program was created to delete Creeper.A program called which is known as Elk Cloner was the first PC virus to appear in the uncultivated that is, outside the single computer or lab where it was created by Richard Skrenta, it attached itself to the orchard apple tree DOS 3.3 operating system and spread via floppy disk disk. This virus, created as a practical joke when Skrenta was studying in the high school and was injected in a game on a floppy disk. On his 50th iterative use the Elk Cloner virus would be activate, which prone to infecting the PCs and displaying a short poem beginning Elk Cloner The program with a personality.The first IBM PC vir us in the natural was a boot sector virus dubbed and created by the Farooq Alvi Brothers in Lahore, Pakistan, seeingly to deter piracy of the software they had written.Before computer networks7 became widespread, most viruses spread on extractable media, particularly floppy disks. In the early days of the PCs, many users frequently exchanged their information and programs on floppies. Some of the viruses are spread by infecting programs which are stored on these disks, while others programs installed themselves into the disk boot sector, which command that they would be run when the user booted the computer from the disk, usually inadvertently. Personal computers of the period would try to boot from the floppy at first if one had been left in the drive. Until floppy disks rejects, this was the most unbeaten transmission system strategy and that is why boot sector viruses were the most parkland in the wild for many years. schematic computer viruses6 emerge in the 1980s, that are driven by the spread of PCs and the consequential addition in BBS, modem use, and software sharing. Bulletin board-driven software giving out contributed directly to the swell of Trojan horse programs, and computer viruses which were written to infect readily traded software. Shareware and bootleg software were equally jet vectors for viruses on BB corpses Viruses can increase their chances of spreading over the several other computers which in networks7 by infecting the files on the particular network file system or a file system which can be accession by other computersMacro viruses have become common since the mid-1990s. Most of these viruses are written in the scripting languages for Microsoft programs such as MS- script and MS-Excel and spread throughout Microsoft Office by infecting documents and spreadsheets. Since Word processor and Excel spread sheets were also available for Mac OS, most could also spread to Macintosh computers. Although most of these computer viruses6 may not have the capability to send contaminated email messages to those viruses which did take advantage of the Microsoft Outlook COM interface.Some old variants of Microsoft Word allow macros to repeat themselves with added blank lines. If two macro viruses concurrently infect a document, the combination of the two, if also self-replicating, can appear as a mating of the two and would likely be detected as a virus unique from the parents.A virus may also send a web address touch on as an instant message to all the contacts on an infected machine. If the recipient, thinking the link is from a friend which isa trusted source follows the link to the website, the virus arrayed at the site may be able to infect this new computer and continue propagating.Viruses that spread using cross-site scripting were first incubateed in 2002, and were academically demonstrated in 2005.There have been multiple instances of the cross-site scripting viruses in the wild, exploiting websites such as MySpace and Yahoo.2.2 classificationIn order to replicate itself, a virus must be permitted to execute code and write to memory. For this reason, many viruses attach themselves to executable files that may be part of legitimate programs (see code injection). If a user attempts to begin an infected program, the virus code may be executed concurrently. Viruses can be uninvolved into two types based on their performance when they are executed. nonresident viruses straight away search for other hosts system or OS which can be infected, or infect those targets, and finally transfer imprint to the application program they infected. Tenant viruses do not search for hosts when they are happening. Instead, a resident virus masses itself into memory on execution and transfers control to the host program. The virus stays active in the background and infects new hosts when those files are accessed by other programs or the operating system itself.2.2.1 Nonresident VirusesNonresident viruses can be notion of as consisting of a viewfinder faculty and a replication module. The finder module is responsible for finding new files to infect. For for separately one new executable file the finder module encounters, it calls the replication module to infect that file.2.2.2 Resident VirusesResident viruses contain a replication module which is parallel to the one that is engaged by nonresident viruses. This section, however, is not called by a finder module. The virus27 masses the extra module into memory when it is executed kinda and en sealeds that this module is executed each while the operating system is called to carry out a definite operation. The replication module can be called, for example, each fourth dimension the operating system executes a file. In this gaffe the virus infects every suitable program that is executed on the computer.Resident viruses are sometimes can be divided into a class of profuse infectors and a class of slow infectors. Fast infectors are those which are knowing to infect as many files as soon as possible. A fast infector, for instance, can infect every potential host file that is accessed. This pose a special difficulty when using anti-virus software1, since a virus scanner will access every prospective host file on a computer when it performs a system-wide scan. If the virus scanner fails to notice that such a virus is present in memory the virus can piggy-back on the virus scanner and in this way infect all files that are scanned. Fast infectors intrust on their fast transmittance rate to spread. The disadvantage of this method is that infecting many files may make detection more likely, because the virus may slow down a computer or perform many risible actions that can be noticed by anti-virus software. Slow infectors, on the other hand, are designed to infect hosts infrequently. Some slow infectors, for instance, only infect files when they are copied. Slow infectors are designed to avoid detection by li miting their actions they are less likely to slow down a computer noticeably and will, at most, infrequently trigger anti-virus software5 that detects suspicious behavior by programs. The slow infector approach, however, does not seem very successful.In most of the operating systems which use file extensions to determine program relations such as Microsoft Windows. The extensions may be normally hidden from the user by default. This makes it probable to create a file that is of a different type than it appears to the users or programmers. For example, an executable file may be created named picture.png.exe, in which the user sees only picture.png and therefore assumes that this file is an image and most likely is safe, yet when opened runs the executable on the client machine.An additional scheme is to generate the virus system from parts of costing operating system files by using the CRC16/CRC32 data. The initial code can be quite small (tens of bytes) and leave off a fairly fu ll-grown virus. This is analogous to a biological prion in the way it works but is vulnerable to signature based detection. This attack has not yet been seen in the wild.2.3 Infection StrategiesVirus avoids detection31 by users, some viruses employ different kinds of deception. Some of the old viruses, especially on the MS-DOS operating system, make sure that the last modified date of a host file stays the same when the file is infected by the virus. This approach does not fool antivirus software, however, especially those which maintain and date cyclic redundancy checks on file changes.Some viruses can infect files without increasing their sizes or damaging the files. They accomplish this by overwriting jobless areas of executable files. These are called cavity viruses. For example, the CIH virus, or Chernobyl Virus, infects Portable Executable files. Because those files have many empty gaps, the virus, which was 1 KB in length, did not add to the size of the file.Some viruses try to avoid detection by killing the tasks associated with antivirus software1 in front it can detect them.As computers and operating systems grow self-aggrandisingr and more complex, old hiding techniques need to be updated or replaced. Defending a computer against viruses may demand that a file system migrate towards detailed and explicit permission for every kind of file access.2.3.1 demo Request InterceptsWhile some antivirus software employ various techniques to counter stealth mechanisms, once the transmittal occurs any recourse to clean the system is unreliable. In Microsoft Windows operating systems, the NTFS file system is proprietary. Direct access to files without using the Windows OS is undocumented. This leaves antivirus software little alternative but to send a read require to Windows OS files that parcel out such requests. Some viruses trick antivirus5 software by intercepting its requests to the OS. A virus can hide itself by intercepting the request to read the infected file, handling the request itself, and return an uninfected version of the file to the antivirus software. The interception can occur by code injection of the actual operating system files that would handle the read request. Thus, an antivirus software1 attempting to detect the virus will either not be given permission to read the infected file, or, the read request will be served with the uninfected version of the same file.File hashes stored in Windows, to identify altered Windows files, can be overwritten so that the System File Checker will report that system files are originals.The only reliable method to avoid stealth is to boot from a spiritualist that is known to be clean. Security software can then be used to check the motionless operating system files. Most security software relies on virus signatures or they employ heuristics, instead of also using a database of file hashes for Windows OS files. Using file hashes to scan for altered files would sanction removin g an infection. The security software can identify the altered files, and request Windows installation media to replace them with authentic versions.2.3.2 Self-ModificationMost modern antivirus programs try to find virus-patterns inside ordinary programs by scanning them for so-called virus signatures. Unfortunately, the term is misleading, in that viruses do not possess unique signatures in the way that human beings do. Such a virus signature is merely a sequence of bytes that an antivirus program looks for because it is known to be part of the virus. A better term would be search strings. Different antivirus programs1 will employ different search strings, and then different search methods, when identifying viruses6. If a virus scanner finds such a pattern in a file, it will perform other checks to make sure that it has found the virus, and not merely a simultaneous sequence in an innocent file, before it notifies the user that the file is infected. The user can then delete, or i n some cases clean or heal the infected file. Some viruses employ techniques that make detection by means of signatures difficult but probably not impossible. These viruses modify their code on each infection. That is, each infected file contains a different variant of the virus.2.3.3 Encryption With A Variable give awayA more advanced method is the use of simple encryption to encipher the virus. In this case, the virus consists of a small decrypting dependent methods and an encrypted copy of the virus code. If the virus is encrypted with the help of different key for each infected file, the only part of the virus that leftovers stable is the decrypting unit, which would (for example) be appended to the end. In this case, a virus scanner will not able to detect directly the virus using signatures, but it can stock-still detect the decrypting unit, which still makes indirect revealing of the virus possible. Since these would be symmetric keys, stored on the infected host. In fact c ompletely possible to decrypt the final virus, but this is almost certainly not required, since self-modifying code is such a scarcity that it may be undercoat for virus scanners to at least oarlock the file as suspicious.This may be old , but solid, encryption involves XORing each byte in a virus with a even, so that the exclusive-or operation has only to be frequent for decryption. It is doubtful for a code to adjust itself, so the code to do the encryption as wll as decryption may be part of the signature in many virus definition.2.3.4 Polymorphic CodePolymorphic code was the first technique that posed a serious threat27 to virus scanners. Likewise various normal encrypted viruses such as a polymorphic virus1516 infects files with an encrypted copy of itself, which may be decoded by a decryption method. In the case of polymorphic viruses or polymorphic worms10, however, this decryption module is also modified on each infection. A well-written polymorphic virus thus has no parts which wait similar between infection, making it very difficult to detect directly using signatures. Antivirus software can detect it by decrypting the viruses using an emulator, or by statistical pattern analysis of the encrypted virus body. To alter polymorphic code, the virus has must have a polymorphic engine which is also called mutating engine or mutation engine anywhere in its encrypted body. Some viruses employ polymorphic code in a system that constrain the change rate of the virus appreciably. For example, a virus can be planned to alter only slightly over time, or it can be programmed to refrain from mutating when it infects a file on a computer that antecedently contains copies of the virus. The benefit of using such sluggish polymorphic1516 code is that it makes it more difficult for antivirus professionals to get representative render of the virus, because tempt files that are infected in one run will naturally have identical or parallel sample of the virus. This wi ll make it more liable that the detection by the virus scanner will be variable, and that some instances of the virus may be able to avoid detection.2.3.5 metamorphous CodeTo avoid being detected by emulation, some viruses revise themselves completely each time they are to infect new executables. Viruses that make use of this technique are said to be metamorphic. To enable metamorphism, a metamorphic engine must be needed. A metamorphic virus is usually very large and complex. For example, W32/Simile consists of over 15,000 lines of assembly language code, 90% of which is part of the metamorphic engine.2.3.6 Avoiding Bait Files and other Undesirable HostsA virus wants to infect hosts in order to multiply further. In some cases, it mogul be a bad idea to infect a mass program. For example, many antivirus softwares perform an integrity check of their own code. Infecting such programs will therefore increase the likelihood that the virus is detected. For this reason, some viruses are programmed not to infect programs that are known to be part of antivirus software. Another type of host that viruses27 sometimes avoid are bait files. Bait files (or goat files) are files that are specially created by antivirus software, or by antivirus professionals themselves, to be infected by a virus. These files can be created for various reasons, all of which are related to the detection of the virusAntivirus professionals can use tempt files to take a attempt of a virus. It is more realistic to store and exchange a small, infected lure file, than to swap a large application program that has been infected by the virus.Antivirus professionals can use bait files to study the actions of a virus and assess detection methods. This is particularly useful when the virus is polymorphic1516. In this case, the virus can be do to infect a large number of entice files. The grimy files can be used to test whether a virus scanner detects all versions of the virus.Some antivirus software e mploy bait files that are accessed rule-governedly. When these files are modified, the antivirus software warns the user that a virus is probably active on the system.Since bait files are used to detect the virus, or to make detection possible, a virus can benefit from not infecting them. Viruses typically do this by avoiding suspicious programs, such as small program files or programs that contain certain patterns of garbage instructions.A related strategy to make baiting difficult is sparse infection. Sometimes, sparse infectors do not infect a host file that would be a suitable candidate for infection in other circumstances. For example, a virus can decide on a random basis whether to infect a file or not, or a virus can only infect host files on particular days of the week.2.4 Vulnerability and Countermeasures2.4.1 The Vulnerability of Operating Systems to VirusesJust as genic diversity in a population decreases the chance of a single disease wiping out a population, the diver sity of software systems on a network similarly limits the destructive potential of viruses. This became a particular concern in the 1990s, when Microsoft gained market dominance in desktop operating systems and office suites. Microsoft software is targeted by virus writers due to their desktop dominance.Although Windows is by far the most popular target operating system for virus writers, viruses also exist on other platforms. Any operating system that allows third-party programs to run can theoretically run viruses.As of 2006, there were at least 60 known security exploits targeting the base installation of Mac OS X (with a Unix-based file system and kernel). The number of viruses6 for the older Apple operating systems, known as Mac OS Classic, varies greatly from source to source, with Apple stating that there are only four known viruses, and independent sources stating there are as many as 63 viruses. many another(prenominal) Mac OS Classic viruses targeted the HyperCard author ing environment. The discrepancy in virus vulnerability between Macs and Windows is a chief selling point, one that Apple uses in their Get a Mac advertising. In January 2009, Symantec inform the discovery of a Trojan that targets Macs. This discovery did not gain much coverage until April 2009.While Linux, and Unix in general, has always natively blocked normal users from having access to make changes to the operating system environment, Windows users are generally not. This difference has continued partly due to the widespread use of administrator accounts in contemporary versions like XP. In 1997, when a virus for Linux was released-known as Bliss-leading antivirus5 vendors issued warnings that Unix-like systems could fall prey to viruses just like Windows. The Bliss virus may be considered characteristic of viruses-as opposed to worms-on Unix systems. Bliss requires that the user run it explicitly, and it can only infect programs that the user has the access to modify. Unlike Windows users, most Unix users do not log in as an administrator user except to install or configure software as a result, even if a user ran the virus, it could not harm their operating system. The Bliss virus never became widespread, and remains chiefly a query curiosity. Its creator later posted the source code to Usenet, allowing researchers to see how it worked.2.4.2 The Role of Software DevelopmentBecause software is often designed with security features to prevent unauthorized use of system resources, many viruses must exploit software bugs in a system or application to spread. Software development strategies that produce large numbers of bugs will generally also produce potential exploits.2.4.3 Anti-Virus Software and other Preventive MeasuresMany users install anti-virus software that can detect and eliminate known viruses after the computer downloads or runs the executable. There are two common methods that an anti-virus software application uses to detect viruses. The fi rst, and by far the most common method of virus detection is using a list of virus signature definitions. This works by examining the content of the computers memory (its RAM, and boot sectors) and the files stored on fixed or removable drives (hard drives, floppy drives), and comparing those files against a database of known virus signatures. The disadvantage of this detection32 method is that users are only protected from viruses that pre-date their last virus definition update. The second method is to use a heuristic algorithm to find viruses based on common behaviors. This method has the ability to detect novel viruses that anti-virus security7 firms have yet to create a signature for.Some anti-virus programs are able to scan opened files in addition to sent and received email messages on the fly in a similar manner. This practice is known as on-access scanning. Anti-virus software does not change the underlying capability of host software to transmit viruses. Users must update their software regularly to charm security holes. Anti-virus software also needs to be regularly updated in order to recognize the up-to-the-minute threats27.One may also minimize the damage done by viruses by making regular backups of data (and the operating systems) on different media, that are either kept unconnected to the system (most of the time), read-only or not accessible for other reasons, such as using different file systems. This way, if data is illogical through a virus, one can start again using the backup (which should preferably be recent).If a backup session on optical media like CD and DVD is closed, it becomes read-only and can no longer be affected by a virus (so long as a virus or infected file was not copied onto the CD/DVD). Likewise, an operating system on a bootable CD can be used to start the computer if the installed operating systems become unusable. Backups on removable media must be carefully inspected before restoration. The Gammima virus, for examp le, propagates via removable flash drives.2.4.4 Recovery MethodsA number of recovery options exist after a computer has a virus. These actions depend on the virus. Some may be safely removed by functions available in most anti-virus software products. Others may require re-installation of damaged programs. It is undeniable to know the characteristics of the virus involved to take the correct action, and anti-virus products will identify known viruses precisely before trying to dis-infect a computer otherwise such action could itself cause a lot of damage. new viruses that anti-virus researchers have not yet studied therefore present an ongoing problem, which requires anti-virus packages1 to be updated frequently.2.4.5 Virus removalOne possibility on Windows Me, Windows XP, Windows Vista and Windows 7 is a tool known as System Restore, which restores the registry and critical system files to a previous checkpoint. Often a virus will cause a system to hang, and a subsequent hard re boot will render a system restore point from the same day corrupt. Restore points from previous days should work provided the virus is not designed to corrupt the restore files and does not exist in previous restore points. Some viruses hamper System Restore and other important tools such as Task Manager and Command Prompt. An example of a virus that does this is Cia Door. Many such viruses can be removed by rebooting the computer, entering Windows safe mode , and then using system tools.Many websites run by anti-virus software companies provide unembellished online virus scanning, with limited cleaning facilities (the purpose of the sites is to sell anti-virus products). Some websites allow a single suspicious file to be checked by many antivirus programs in one operation. Additionally, several capable antivirus software programs are available for free download from the internet (usually restricted to non-commercial use), and Microsoft provide a free anti-malware expediency that runs as part of their regular Windows update regime.2.4.6 Operating System ReinstallationReinstalling any OS is another stew to virus removal. It involves either reformatting the computers hard disk drive and installing the operating system and