For 19 years, Windows’ Achilles heel has been its vulnerability to viruses. In my opinion, this vulnerability is ridiculously overstated (especially by the competition), but it is a liability. Unfortunately, most anti-virus software is either awful, expensive, or both.
With this in mind, I am astonished that it took Microsoft so long to develop its own anti-virus software to maximize the performance of Windows while still protecting users from malicious code.
As of today, Microsoft has remedied its omission, and you can download its free Security Essentials software. If you are using industrial-strength anti-virus software, you may not want to switch. But if you are still paying for MacAfee or Norton, give Security Essentials a try. I am running it on my system, and so far, so god, even with background detection running (which I did not bother with when I used AVG because of the performance hit).