Antivirus software are computer programs that attempt to identify, neutralize or eliminate malicious software. The term "antivirus" is used because the earliest examples were designed exclusively to combat computer viruses; however most modern antivirus software is now designed to combat a wide range of threats, including worms, phishing attacks, rootkits, trojan horses and other malware. Antivirus software typically uses two different approaches to accomplish this:

Scanning files to look for known viruses matching definitions in a virus dictionary, and identifying suspicious behavior from any computer program which might indicate infection.

The second approach is called heuristic analysis. Such analysis may include data captures, port monitoring and other methods.

Most commercial antivirus software uses both of these approaches, with an emphasis on the virus dictionary approach. Some people consider network firewalls to be a type of antivirus software, however this is not correct.

Dictionary :

In the virus dictionary approach, when the antivirus software looks at a file, it refers to a dictionary of known viruses that the authors of the antivirus software have identified. If a piece of code in the file matches any virus identified in the dictionary, then the antivirus software can take one of the following actions:

Attempt to repair the file by removing the virus itself from the file.
Quarantine the file (such that the file remains inaccessible to other programs and its virus can no longer spread)
Delete the infected file.
To achieve consistent success in the medium and long term, the virus dictionary approach requires periodic (generally online) downloads of updated virus dictionary entries. As civically-minded and technically-inclined users identify new viruses "in the wild", they can send their infected files to the authors of antivirus software, who then include information about the new viruses in their dictionaries.

Dictionary-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. Note too that a System Administrator can typically schedule the antivirus software to examine (scan) all files on the computer's hard disk on a regular basis.

Issues of concern :

The regular appearance of new malware is certainly in the financial interest of vendors of commercial antivirus software, but there is no evidence of collusion.

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 — often at the cost of slower performance.

It is important to note that one should not have more than one memory-resident antivirus software solution installed on a single computer at any given time. Otherwise, the computer may be crippled and further damaged.

It is sometimes necessary to temporarily disable virus protection when installing major updates such as Windows Service Packs or updating graphics card drivers.Active antivirus protection may partially or completely prevent the installation of a major update.

When purchasing antivirus software, the agreement may include a clause that your subscription will be automatically renewed, and your credit card automatically billed at the renewal time without your approval. For example, McAfee requires one to unsubscribe at least 60 days before the expiration of the present subscription.In that case, the subscriber may contest the charges with the credit card issuer, but this recourse is likely to fail if in fact the subscriber had authorised such a "continuous payment authority". Norton Antivirus also has a default setting that includes the automatic renewal of your subscription.

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.

Some commercial antivirus software programs contain adware. For example, the home/small business version of CA Anti-Virus 2008 displays an advert for CA products whenever the desktop is unlocked after a period of inactivity.

Most widely-accepted antivirus programs often do not detect newly-created viruses. This can be verified by making a program with destructive code in a language like C++.

Anti-virus manuafacturers have been criticised for fear mongering by exaggerating the risk that virus pose to consumers.

Mobile devices :

Viruses from the desktop and laptop world have migrated to 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.