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Antivirus software (or anti-virus) is computer software used to identify and remove computer viruses, as well as many other types of harmful computer software, collectively referred to as malware. While the first antivirus software was designed exclusively to combat computer viruses, most modern antivirus software can protect against a wide range of malware, including worms, rootkits, trojans and lots of more harmful object.
History
There are competing claims for the innovator of the first antivirus product. Perhaps the first publicly-known neutralization of a wild PC virus was performed by Bernt Fix (also Bernd) in early 1987. Fix neutralized an infection of the Vienna virus.[1] [2] The first edition of a antivirus program to detect and repair the cipap mks_vir was released in 1987; the program was only available with a Polish interface. Autumn 1988 saw antivirus software Dr. Solomon's Anti-Virus Toolkit released by Briton Alan Solomon. Also in 1988 AIDSTEST and AntiVir were released. By December 1990, the market had matured to the point of nineteen separate antivirus products being on sale including Norton AntiVirus and VirusScan from McAfee.
Peter Tippett made a number of contributions to the budding field of virus detection.[3] He was an emergency-room doctor who also ran a computer software company. He had read an article about the Lehigh virus and questioned whether, from an epidemiological viewpoint, they would have similar characteristics to biological viruses that attack organisms. The IBM compatible computers had various vulnerabilities. The boot sector was affected by the Brain virus, and within IBM DOS and MS-DOS, executable files, with either EXE filename extension or COM file extension, were affected by the Jerusalem virus) and the Lehigh virus specifically targeted .com files. Tippett’s company Certus International Corp. then began to sell anti-virus software programs. The company was sold in 1992 to Symantec Corp, and Tippett went to work for them, incorporating the software he had developed into Symantec’s product, Norton AntiVirus.[citation needed]
Before Internet connectivity was widespread, viruses were typically spread by infected floppy disks; antivirus software started to be used, but was updated relatively infrequently. At that time it was said, correctly, that viruses could not be spread by the readable content of emails, although executable attachments were as risky as programs on floppy disks. Virus checkers essentially had to check executable files, and the boot sectors of floppy and hard disks. As Internet usage became common, initially by making a modem connection when desired, viruses spread through the Internet.
Powerful macros in word processors such as Microsoft Word presented a further risk. Virus writers started using the macros to write viruses that attached themselves to documents; this meant that computers could now also be at risk from infection by documents (with hidden attached macros) as programs. Later email programs, in particular Microsoft Outlook Express and Outlook, became able to execute program code from within a message's text by simply reading the message, or even previewing its content. Virus checkers now had to check many more types of file. As broadband always-on 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 virus could spread widely before it was detected, identified, a checker update released, and virus checkers round the world updated.
A very uncommon use of the term "antivirus" is to apply it to benign viruses that spread and combated malicious viruses. This was common on the Amiga computer platform.
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.
Malicious activity detection is another way to identify malware. In this approach, antivirus software monitors the system for suspicious program behavior. If suspicious behavior is detected, the suspect program may be further investigated, using signature based detection or another method listed in this section. This type of detection can be used to identify unknown viruses. Heuristic-based detection, like malicious activity detection, can be used to identify unknown viruses. This can be accomplished in one of two ways; file analysis and file emulation. File analysis is the process of searching a suspect file for virus-like instructions. For example, if a program has instructions to format the C drive, antivirus software might further investigate the file. One downside is the amount of computer resources needed to analyze every file. 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.

Signature based detection is the most common method that antivirus software uses to identify malware. This method is somewhat limited by the fact that it can only identify a limited amount of emerging threats, e.g. generic, or extremely broad, signatures.
When antivirus software scans a file for viruses, it checks the contents of a file against a dictionary of virus signatures. A virus signature is the viral code. Finding a virus signature in a file is the same as saying you found the virus itself. If a virus signature is found in a file, the antivirus software can take action to remove the virus. Antivirus software will usually perform one or more of the following actions; quarantining, repairing, or deleting. Quarantining a file will make it inaccessible, and is usually the first action antivirus software will take if a malicious file is found. Encrypting the file is a good quarantining technique because it renders the file useless.
Sometimes a user wants to save the content of an infected file because viruses can sometimes embed themselves in files, called code injection, and the file may be essential to normal operation. To do this, antivirus software will attempt to repair the file. To do this, the software will try to remove the viral code from the file. Unfortunately, some viruses might damage the file upon injection.
The third action antivirus software can take against a virus is deleting it. If a file repair operation fails, usually the best thing to do is to just delete the file. Deleting the file is necessary if the entire file is infected.
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. There, the virus can be analyzed and the signature added to the dictionary.
Signature-based antivirus software typically examines files when the computer's operating system creates, opens, closes, or e-mails them. In this way it can detect a known virus immediately upon receipt. System administrators can schedule antivirus software to scan all files on the computer's hard disk at a set time and date.
Although the signature based approach can effectively contain virus outbreaks in the right circumstances, 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.
An emerging technique to deal with malware in general is whitelisting. Rather than looking for only known bad software, this technique prevents execution of all computer code except that which has been previously identified as trustworthy by the system administrator. By following this "default deny" approach, the limitations inherent in keeping virus signatures up to date are avoided. Additionally, computer applications that are unwanted by the system administrator are prevented from executing since they are not on the whitelist. Since modern enterprise organizations have large quantities of trusted applications, the limitations of adopting this technique rests with the system administrators' ability to properly inventory and maintain the whitelist of trusted applications. Viable implementations of this technique include tools for automating the inventory and whitelist maintenance processes.

The suspicious behavior approach, by contrast, does not attempt to identify known viruses, but instead monitors the behavior of all programs. If one program tries to write data to an executable program, for example, the antivirus software can flag this suspicious behavior, alert a user, and ask what to do.
Unlike the signature based approach, the suspicious behavior approach therefore provides protection against brand-new viruses that do not yet exist in any virus dictionaries. However, it can also sound a large number of false positives, and users may become desensitized to the warnings. If the user clicks "Accept" on every such warning, then the antivirus software obviously gives no benefit to that user. This problem has worsened since 1997[citation needed], since many more non-malicious program designs came to modify other .exe files without regard to this false positive issue. In recent years, however, sophisticated behavior analysis has emerged, which analyzes processes and calls to the kernel in context before making a decision, which gives it a lower false positive rate than rules based behavior monitoring.

Some more sophisticated antivirus software uses heuristic analysis to identify new malware. Two methods are used; file analysis and file emulation.
As described above, file analysis is the process by which antivirus software will analyze the instructions of a program. Based on the instructions, the software can determine whether or not the program is malicious. For example, if the file contains instructions to delete important system files, the file might be flagged as a virus. While this method is useful for identifying new viruses and variants, it can trigger many false positives.
The second heuristic approach is file emulation. By the this approach, the target file is run in a virtual system environment, separate from the real system environment. The antivirus software would then log what actions the file takes in the virtual environment. If the actions are found to be damaging or malicious, the file may be marked a virus. But again, this method can trigger false positives.

Many viruses start as a single infection, and through either mutation or refinements by other attackers, can grow into dozens of slightly different strains. Generic detection refers to the detection and removal of multiple threats using a single virus definition. [4]
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".
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 create a single generic signature. These signatures often contain non-contiguous code, using wild cards where differences lie. These wild cards allow the scanner to detect if virus code is padded with code. [5]
Virus removal tools
A virus removal tool is software for removing specific viruses from infected computers. Unlike complete antivirus scanners, they are usually not intended to detect and remove an extensive list of viruses; rather they are designed to remove specific viruses, usually more effectively than normal antivirus software. Examples of these tools include McAfee Stinger and the Microsoft Malicious Software Removal Tool (which is run automatically by Windows update). Many of these tools are available for free download.
These tools can sometimes do a better job of removing a specific virus than conventional antivirus software.

Issues of concern
Some antivirus software can considerably reduce performance. Users may disable the antivirus protection to overcome the performance loss, thus increasing the risk of infection. For maximum protection, the antivirus software needs to be enabled all the time[citation needed] — often at the cost of slower performance (see also software bloat).

Antivirus programs can in themselves pose a security risk as they often run at the 'System' level of privileges and may hook the kernel — Both of these are necessary for the software to effectively do its job, however exploitation of the antivirus program itself could lead to privilege escalation and create a severe security threat. Arguably, use of antivirus software when compared to Principle of least privilege is largely ineffective when ramifications of the added software are taken into account.
When purchasing antivirus software, the agreement may 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 one to unsubscribe at least 60 days before the expiration of the present subscription.[6] Norton Antivirus also renews subscriptions automatically by default. [7].

Cloud computing is a new concept in technology that works in the clouds of the Internet IT Infrastructure. Researchers, Jon Oberheide, Evan Cooke, and Farnam Jahanian, from the University of Michigan CloudAv explain their project:
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 the researchers built uses 12 different detectors that act together to tell the PC whether the item is safe to open. [8]
In current anti-virus 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 anti-virus and behavioral detection simultaneously. It is more thorough and also has the ability to check the new document or programs access history.

Some antivirus programs are actually spyware masquerading as antivirus software. It is best to double-check that the antivirus software which is being downloaded is actually a real antivirus program.[9]

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.[10]

Running multiple antivirus programs concurrently can harm performance and create conflicts.[11] It is sometimes necessary to temporarily disable virus protection when installing major updates such as Windows Service Packs or updating graphics card drivers.[12] Active antivirus protection may partially or completely prevent the installation of a major update.
Mobile devices
Viruses from the desktop and laptop world have either migrated to, or are assisted in their dispersal by mobile devices. Antivirus vendors are beginning to offer solutions for mobile handsets. These devices present significant challenges for antivirus software, such as processor constraints, memory constraints, and definitions and new signature updates to these mobile handsets.
Mobile handsets are now offered with a variety of interfaces and data connection capabilities. Consumers should carefully evaluate security products before deploying them on devices with a small form factor.
Solutions that are hardware-based, perhaps USB devices or SIM-based antivirus solutions, might work better in meeting the needs of mobile handset consumers. Technical evaluation and review on how deploying an antivirus solution on cellular mobile handsets should be considered as scanning process might impact other legitimate applications on the handheld.
SIM-based solutions with antivirus integrated on the small memory footprint might provide a basic solution to combat malware/viruses in protecting PIM and mobile user data. Solutions based on USB and Flash memory allow the user to swap and use these products with a range of hardware devices.
Effectiveness
Studies in December 2007 have shown that the effectiveness of Antivirus software is much reduced from what it was a few years ago, particularly against unknown or zero day threats. The German computer magazine c't found that detection rates for these threats had dropped to a frightening 20% to 30%, as compared to 40% to 50% only one year earlier. At that time only one product managed a detection rate above 50%.[13]
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-up screen messages. Modern viruses are often written by professionals, financed by criminal organizations.[14] It is not in their interests to make their viruses or crimeware evident, because their purpose is to create botnets or steal information for as long as possible without the user realizing this; consequently, they are often well-hidden. If an infected user has a less-than-effective antivirus product that says the computer is clean, then the virus may go undetected.
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 publicized 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 utilised by a few antivirus solutions is whitelisting, this technology first checks if the file is trusted and only questioning those that are not.[15] With the addition of wisdom of crowds, antivirus solutions backup other antivirus techniques by harnessing the intelligence and advice of a community of trusted users to protect each other. By providing these multiple layers of malware protection and combining them with other security software it is possible to have more effective protection from the latest zero day attack and the latest crimeware than previously was the case with just one layer of protection.
List of Top Antivirus Softwares
BitDefender
Avast!
AVG Anti-Virus
Avira
BullGuard
CA Anti-Virus
Cisco Security Agent
DriveSentry (antivirus, antispyware and HIPS technologies)
eSafe
Fortinet FortiClient End Point Security
F-PROT
F-Secure
G DATA Software
Kaspersky Anti-Virus
LinuxShield
McAfee VirusScan
nProtect
NOD32
Norman ASA
Norton AntiVirus/Norton 360
Panda Security
PC Tools AntiVirus
Rising AntiVirus
Sophos Anti-Virus
Trend Micro Internet Security
Vba32 AntiVirus
Windows Live OneCare
ZoneAlarm
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