Computer viruses are increasingly sophisticated and pervasive. If you can't afford to run your computer without some sort of antivirus software installed, check out these five popular options to protect your PC.

Photo by Cushing Memorial Library and Archives, Texas A&M University Archives.

Earlier this week we asked you to share your favorite antivirus application; now we're back with the five most popular apps to help you secure your PC and keep it running virus free.

Note: For each entry, we reviewed the lowest cost option available from the company in question. Most companies offer premium packages of varying cost and with varying additional bells and whistles, save for the always-free Micrsoft Security Essentials. For the purpose of this comparison, we stuck to the free/entry level options.

Having just celebrated its 21st birthday, Avast! is an old player in the antivirus market. Avast! has built up a solid following based on their philosophy of offering dependable and effective antivirus protection