The most important thing you want to know is how good the program is at detecting computer viruses. One way of determining the virus detection rate of a program is to use the free version. Another, is to rely on expert opinion in the form of reviews of these software programs provided online. Many computer magazines provide a review of the best antivirus programs, by running benchmark tests.

Check out specific comparisons made between programs or brands, like the Avast vs AVG comparison made in this Buzzle article. Go for antivirus engines which offer a solid track record in terms of virus detection. Opt for a program that uses the system resources without slowing it down too much. Make sure that the program has a rootkit virus detection tool and a registry cleaner.