Let's start with what Anti-Virus do I use to protect myself? I use Kaspersky Anti-Virus and ESET NOD32  on my business machines for real time virus scanning (one or the other per machine, do not install more than one anti-virus solution per machine). The reasons I have chosen Kaspersky and Nod32 are that they are simple, quick they update their definitions more frequently than they're competitors. Not to mention that historically both have been proven to be quicker to identify new threats.

Statistically they know sooner what is a threat and they tell me sooner than the top market share holders anti-virus providers. In my experience they scan faster, use less system resources and cost less than the market share leading comptetitors.

If you are wondering about all the Free Virus Scanning software available? I frequently encounter systems running up to date free antivirus solutions that are virus infected or are experiencing software conflicts rendering the machine virtually unusable. When it comes to anti-virus software you get what you pay for, I guarantee you will spend more getting a virus removed once than it would have cost you to have had protected yourself effectively with a reliable solution.