An anti-virus software program is a computer program that can be used to scan files to identify and eliminate computer viruses and other malicious software (malware).

Free antivirus programs vary just as much as paid security programs do in the quality of their protection. And frugal computer users on the hunt for no-cost antivirus software--already faced with tons of options. While free antivirus programs give you some value, they don't have everything that a paid security application can offer.

For one thing, you won't have anyone to call if things go haywire, or if you need disinfection help in the event something does sneak past your PC's defences. Most free apps give support only on online forums, though Avast offers e-mail support (and Microsoft plans to when Security Essentials launches); Avast users can submit online support tickets, too. AVG gives paid phone support, but the $50-per-call fee costs more than most paid antivirus apps.

Finally, some free programs give you stuff you don't want. Some of the apps gives you both default to installing unnecessary search or social networking browser toolbars (you can opt out during program installation), and many free apps display ads urging you to buy the paid versions. Avira's daily pop-up ads are the most intrusive, but Avast, AVG, and PC Tools Antivirus Free Edition all display ads in some form as well.