Antivirus software
From Wikipedia, the free encyclopedia
Antivirus (or anti-virus) software is used to prevent, detect, and remove malware, including computer viruses, worms, and trojan horses. Such programs may also prevent and remove adware, spyware, and other forms of malware.
A variety of strategies are typically employed. Signature-based detection involves searching for known malicious patterns in executable code. However, it is possible for a user to be infected with new malware for which no signature exists yet. To counter such so-called zero-day threats, heuristics can be used. One type of heuristic approach, generic signatures, can identify new viruses or variants of existing viruses by looking for known malicious code (or slight variations of such code) in files. Some antivirus software can also predict what a file will do if opened/run by emulating it in a sandbox and analyzing what it does to see if it performs any malicious actions. If it does, this could mean the file is malicious.
However, no matter how useful antivirus software is, it can sometimes have drawbacks. Antivirus software can degrade computer performance. Inexperienced users may have trouble understanding the prompts and decisions that antivirus software presents them with. An incorrect decision may lead to a security breach. If the antivirus software employs heuristic detection (of any kind), success depends on achieving the right balance between false positives and false negatives. False positives can be as destructive as false negatives. Finally, antivirus software generally runs at the highly trusted kernel level of the operating system, creating a potential avenue of attack.[1]
In addition to the drawbacks mentioned above, the effectiveness of antivirus software has also been researched and debated. One study found that the detection success of major antivirus software dropped over a one-year period.[2]
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[edit] History
Most of the computer viruses that were written in the early and mid '80s were limited to self-reproduction and had no specific damage routine built into the code (research viruses[3]). That changed when more and more programmers became acquainted with virus programming and released viruses that manipulated or even destroyed data on infected computers. It then became necessary to think about antivirus software to fight these malicious viruses.
There are competing claims for the innovator of the first antivirus product. Possibly the first publicly documented removal of a computer virus in the wild was performed by Bernd Fix in 1987.[4][5]
Fred Cohen, who published one of the first academic papers on computer viruses in 1984[6], started to develop strategies for antivirus software in 1988
Also in 1988 a mailing list named VIRUS-L[7] was initiated on the BITNET/EARN network where new viruses and the possibilities of detecting and eliminating viruses were discussed. Some members of this mailing list like John McAfee or Eugene Kaspersky later founded software companies that developed and sold commercial antivirus software.
Before Internet connectivity was widespread, viruses were typically spread by infected floppy disks. Antivirus software came into use, but was updated relatively infrequently. During this time, virus checkers essentially had to check executable files and the boot sectors of floppy and hard disks. However, as internet usage became common, initially through the use of modems, viruses spread throughout the Internet.[8]
Over the years antivirus software had to check many more types of files (and not only executable files) for several reasons:
- Powerful macros used in word processor applications, such as Microsoft Word, presented a further risk. Virus writers started using the macros to write viruses embedded within documents. This meant that computers could now also be at risk from infection by documents with hidden attached macros as programs.[9]
- Later email programs, in particular Microsoft Outlook Express and Outlook, were vulnerable to viruses embedded in the email body itself. Now, a user's computer could be infected by just opening or previewing a message.[10]
As always-on broadband connections became the norm and more and more viruses were released, it became essential to update virus checkers more and more frequently. Even then, a new zero-day virus could become widespread before antivirus companies released an update to protect against it.
[edit] Identification methods
There are several methods which antivirus software can use to identify malware.
Signature based detection is the most common method. To identify viruses and other malware, antivirus software compares the contents of a file to a dictionary of virus signatures. Because viruses can embed themselves in existing files, the entire file is searched, not just as a whole, but also in pieces.[11]
Heuristic-based detection, like malicious activity detection, can be used to identify unknown viruses.
File emulation is another heuristic approach. File emulation involves executing a program in a virtual environment and logging what actions the program performs. Depending on the actions logged, the antivirus software can determine if the program is malicious or not and then carry out the appropriate disinfection actions.[12]
[edit] Signature based detection
Traditionally, antivirus software heavily relied upon signatures to identify malware. This can be very effective, but cannot defend against malware unless samples have already been obtained and signatures created. Because of this, signature-based approaches are not effective against new, unknown viruses.
Because new viruses are being created each day, the signature-based detection approach requires frequent updates of the virus signature dictionary. To assist the antivirus software companies, the software may allow the user to upload new viruses or variants to the company, allowing the virus to be analyzed and the signature added to the dictionary.[11]
Although the signature-based approach can effectively contain virus outbreaks, virus authors have tried to stay a step ahead of such software by writing "oligomorphic", "polymorphic" and, more recently, "metamorphic" viruses, which encrypt parts of themselves or otherwise modify themselves as a method of disguise, so as to not match virus signatures in the dictionary.[13]
[edit] Heuristics
Some more sophisticated antivirus software uses heuristic analysis to identify new malware or variants of known malware.
Many viruses start as a single infection and through either mutation or refinements by other attackers, can grow into dozens of slightly different strains, called variants. Generic detection refers to the detection and removal of multiple threats using a single virus definition.[14]
For example, the Vundo trojan has several family members, depending on the antivirus vendor's classification. Symantec classifies members of the Vundo family into two distinct members, Trojan.Vundo and Trojan.Vundo.B.[15][16]
While it may be advantageous to identify a specific virus, it can be quicker to detect a virus family through a generic signature or through an inexact match to an existing signature. Virus researchers find common areas that all viruses in a family share uniquely and can thus create a single generic signature. These signatures often contain non-contiguous code, using wildcard characters where differences lie. These wildcards allow the scanner to detect viruses even if they are padded with extra, meaningless code. [17] Padded code is used to confuse the scanner so it can't recognize the threat.
A detection that uses this method is said to be "heuristic detection."
[edit] Rootkit detection
Anti-virus software now scans for rootkits; a rootkit is a type of malware that is designed to gain administrative-level control over a computer system without being detected. Rootkits can change how the operating system functions and in some cases, rootkits can tamper with the anti-virus program and render it ineffective. Rootkits are also very difficult to remove, in some cases requiring a complete re-installation of the operating system.[18][19]
[edit] Issues of concern
[edit] Unexpected renewal costs
Some commercial antivirus software end-user license agreements include a clause that the subscription will be automatically renewed, and the purchaser's credit card automatically billed, at the renewal time without explicit approval. For example, McAfee requires users to unsubscribe at least 60 days before the expiration of the present subscription[20] while BitDefender sends notifications to unsubscribe 30 days before the renewal.[21] Norton Antivirus also renews subscriptions automatically by default.[22]
[edit] Rogue security applications
Some antivirus programs are actually malware masquerading as antivirus software, such as WinFixer and MS Antivirus.[23] A recent surge in such software has deceived more than a million Microsoft Windows internet users and prompted the FTC to initiate court proceedings.[citation needed]
[edit] Problems caused by false positives
A false positive is identifying a file as a virus when it is not a virus. If an antivirus program is configured to immediately delete or quarantine infected files (or does this by default), false positives in essential files can render the operating system or some applications unusable.[24] In May 2007, a faulty virus signature issued by Symantec mistakenly removed essential operating system files, leaving thousands of PCs unable to boot.[25] Also in May 2007 the executable file required by Pegasus Mail was falsely detected by Norton AntiVirus as being a Trojan and it was automatically removed, preventing Pegasus Mail from running.[26] Norton anti-virus has falsely identified three releases of Pegasus Mail as malware; Norton anti-virus can delete the Pegasus Mail installer file when this happens.[27] In response to this Pegasus Mail stated:
| “ | On the basis that Norton/Symantec has done this for every one of the last three releases of Pegasus Mail, we can only condemn this product as too flawed to use, and recommend in the strongest terms that our users cease using it in favour of alternative, less buggy anti-virus packages.[27] | ” |
In April 2010 McAfee VirusScan detected svchost.exe, a normal Windows binary, as a virus on machines running XP SP3 and removed it, causing a reboot loop and loss of all network access.[28][29]
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Running multiple antivirus programs concurrently can degrade performance and create conflicts.[30]
It is sometimes necessary to temporarily disable virus protection when installing major updates such as Windows Service Packs or updating graphics card drivers.[31] Active antivirus protection may partially or completely prevent the installation of a major update.
Support issues also exist around antivirus application interoperability with common solutions like SSL VPN remote access and network access control products.[32] Often, these technology solutions have policy assessment applications which require that 1. an antivirus is installed 2. that the product is running and 3. that the application's signatures are up to date. If the antivirus application is not recognized by the policy assessment, whether because the antivirus application has been updated or because it is not part of the policy assessment library, the user will be unable to connect. Interoperability testing and certification for antivirus applications is offered by the OESIS OK Program.[33]
[edit] Effectiveness
Studies in December 2007 have shown that the effectiveness of antivirus software has decreased in recent years, particularly against unknown or zero day attacks. The German computer magazine c't found that detection rates for these threats had dropped from 40-50% in 2006 to 20-30% in 2007. At that time, the only exception was the NOD32 antivirus, which managed a detection rate of 68 percent.[2]
The problem is magnified by the changing intent of virus authors. Some years ago it was obvious when a virus infection was present. The viruses of the day, written by amateurs, exhibited destructive behavior or pop-ups. Modern viruses are often written by professionals, financed by criminal organizations.[34]
Traditional antivirus software solutions run virus scanners on schedule, on demand and some run scans in real time. If a virus or malware is located the suspect file is usually placed into a quarantine to terminate its chances of disrupting the system. Traditional antivirus solutions scan and compare against a publicised and regularly updated dictionary of malware otherwise known as a blacklist. Some antivirus solutions have additional options that employ an heuristic engine which further examines the file to see if it is behaving in a similar manner to previous examples of malware. A new technology utilized by a few antivirus solutions is whitelisting, this technology first checks if the file is trusted and only questioning those that are not.[35]
Independent testing on all the major virus scanners consistently shows that none provide 100% virus detection. The best ones provided as high as 99.6% detection, while the lowest provide only 81.8% in tests conducted in February 2010. All virus scanners produce false positive results as well, identifying benign files as malware.[36]
Although methodologies may differ, some notable independent quality testing agencies include AV-Comparatives, ICSA Labs, West Coast Labs, VB100 and other members of the AMTSO (Anti-Malware Testing Standards Organization).[37]
[edit] New viruses
Most popular anti-virus programs are not very effective against new viruses, even those that use non-signature-based methods that should detect new viruses. The reason for this is that the virus designers test their new viruses on the major anti-virus applications to make sure that they are not detected before releasing them into the wild.[38]
Some new viruses, particularly ransomware, use polymorphic code to avoid detection by virus scanners. Jerome Segura, a security analyst with ParetoLogic, explained:[39]
| “ | It's something that they miss a lot of the time because this type of [ransomware virus] comes from sites that use a polymorphism, which means they basically randomize the file they send you and it gets by well-known antivirus products very easily. I've seen people firsthand getting infected, having all the pop-ups and yet they have antivirus software running and it's not detecting anything. It actually can be pretty hard to get rid of, as well, and you're never really sure if it's really gone. When we see something like that usually we advise to reinstall the operating system or reinstall backups.[39] | ” |
[edit] Rootkits
The detection of rootkits are a major challenge for anti-virus programs. Rootkits are extremely difficult to detect and if undetected, rootkits have full administrative access to the computer and are invisible to users e.g. a rootkit will not be shown in the list of running processes in the task manager. Rootkits can modify the inner workings of the operating system[40] and tamper with the anti-virus program.[41] If a rootkit hides itself in firmware e.g. the motherboard BIOS, it may never be discovered[42] and could persist even if the operating system is cleanly installed on a reformatted or new hard drive.[43][44]
[edit] Other methods
Installed antivirus software running on an individual computer is only one method of guarding against viruses. Other methods are also used, including cloud-based antivirus, firewalls and on-line scanners.
[edit] Cloud antivirus
In current antivirus software a new document or program is scanned with only one virus detector at a time. CloudAV would be able to send programs or documents to a network cloud where it will use multiple antivirus and behavioural detection simultaneously. It is more thorough and also has the ability to check the new document or programs access history.[45]
CloudAV is a cloud computing antivirus developed as a product of scientists of the University of Michigan. Each time a computer or device receives a new document or program, that item is automatically detected and sent to the antivirus cloud for analysis. The CloudAV system uses 12 different detectors that act together to tell the PC whether the item is safe to open.[45][46][47]
[edit] Network firewall
Network firewalls prevent unknown programs and Internet processes from accessing the system protected. However, they are not antivirus systems as such and thus make no attempt to identify or remove anything. They may protect against infection from outside the protected computer or LAN, and limit the activity of any malicious software which is present by blocking incoming or outgoing requests on certain TCP/IP ports. A firewall is designed to deal with broader system threats that come from network connections into the system and is not an alternative to a virus protection system.
[edit] Online scanning
Some antivirus vendors maintain websites with free online scanning capability of the entire computer, critical areas only, local disks, folders or files.
[edit] Specialist tools
Virus removal tools are available to help remove stubborn infections or certain types of infection. Examples include the Trend Micro Rootkit Buster[48] for the detection of rootkits and VundoFix for removing some variations of Vundo infections. Anti-virus vendors also offer tools to remove virus infections, such as the Avira AntiVir Removal Tool.[49]
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