Antivirus Software


How antivirus programs work


Antivirus (AV) is a term applied to either a single program or a collection of programs that serve to protect a computer system from viruses. The main component of an antivirus solution is the scanning engine (for an on-screen example, see here). The intricate details of each engine vary, but all share the basic responsibility of identifying virus-laden files using virus signature files: a unique string of bytes that identifies the virus like a fingerprint. They view patterns in the data and compare them to traits of known viruses captured in the wild to determine if a file is infected, and in most cases are able to strip the infection from files, leaving them undamaged. When repairs aren't possible, antivirus programs will quarantine the file to prevent accidental infection, or can be set up to delete the file immediately.

In the case of new viruses for which no antidote has been created, some engines also use heuristic scanning. This allows the AV programs to flag suspicious data structures or unusual virus-like activity even when there is no matching virus definition. If the program sees any funny business, it quarantines the questionable program and broadcasts a warning to you about what the program may be trying to do (such as modify your Windows Registry). The accuracy of such methods is much lower however, and often a program with this running may err on the side of caution. This can result in confusing false positive results.

If you and the software think the program may be a virus, you can send the quarantined file to the antivirus vendor, where researchers examine it, determine its signature, name and catalog it, and release its antidote. It's now a known virus.


What does AV software protect me from?

The levels of protection vary according to the age of the antivirus product. Newer products include automatic update functions, scheduled scans, memory resident protection and integration with Internet applications such as e-mail clients and Web browsers. Older antivirus products may only consist of a scanner that needs to be manually operated. All virus scanners will protect your PC from viruses if used correctly to regularly scan the hard disks, removable media (such as USB drives, Firewire devices, floppy or Zip disks) as they are loaded into the PC, or any downloaded files prior to use. (Note: If you use a USB key from an infected computer on your PC, that does not mean you will get the virus too. However, you will if you run the infected applications from the USB drive.)

Where the new products shine is in their ability to protect PCs even when the owners aren't as careful as they should be. They include automatic removable media scanning options, helpful reminders when the virus definitions are dangerously out of date (see example here) and integration with existing Internet browsers and email applications. Some even automatically scan common file-dumping grounds like the desktop, ensuring that even if other measures aren't configured they still get to scan files before anything untoward happens.

At a minimum, you should be able to expect protection from boot-sector viruses, macro viruses, Trojans, executable files with viruses and worms. With new products you should also expect to find protection from malicious Web pages, scripts, ActiveX controls, Java applets and e-mail worms. Look for products with spyware support for additional protection.


Differences between AV solutions

Fundamentally, all antivirus packages do the same thing - they keep your computer virus-free by scanning and cleaning files. Many of them even share the same integral scanning engine to identify viruses. The main differences come in the polish of the graphical user interface (GUI), the number of add-on functions (e-mail scanners, scheduled automatic updates, heuristic scanning, antispyware etc.) and in the speed and accuracy of the product.


The usability of an antivirus program is essential for its ongoing success. If the pop-ups aren't friendly, then they'll quickly be disabled in options. If the system tray program is unstable, it will be switched off and unless the updates are quick and easy, they'll get neglected. Make certain the GUI works for you before you buy, and check with other people for their opinions on the stability of the products they have used. A memory-resident scanner with just a few nasty bugs in it for example, can cause all kinds of problems with using and copying files or just keeping your system stable.

Some antivirus vendors are now bundling their antivirus products with personal firewalls and Web filters to create "Security Suites", but they aren't necessary to just keep a system virus-free. Check that the extra features one product has over another are actually something you'll use as opposed to a neat marketing gimmick.

As for the speed and accuracy comparison, there are big differences between the vendors. For a thorough guide on AV software, take a look at http://AV-test.org .


What is an online virus scanner?

Online virus scanners are free web sites provided by antivirus vendors to scan computers for viruses over the Internet. They are often functionally limited to scanning only certain types of files and most do not offer cleaning or repair functions. Their use is limited to providing piece-of-mind to users without full antivirus programs of their own and detecting a virus with one will usually result in an invitation to buy the vendors full product online.


Why would I want a personal firewall included?

Any computer connected to a broadband link without a firewall of some kind is almost certainly infected. Recent research has shown an average time of around eight minutes from connection to the Internet to being infected by worms for unprotected and unpatched Windows XP systems. Many commercial antivirus products can be purchased bundled with personal firewall products that filter the computer's Internet traffic and reject attacks. In the case of Norton AntiVirus 2005 a cut-down version of their personal firewall software is installed by default with a set of definitions for repelling worm attacks.

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