App 11: Microsoft Security Essentials

Ever since computers have started using the internet, we have been worried about malware and viruses. It's always recommended to keep your computer protected with some sort of anti-virus program. However, with so much involved with virus-scanning (like real-time protection, attachment scanning, updates and registry scanning) some programs can end up slowing down your computer considerably.

Thats why I recommend Microsoft Security Essentials, when it comes to protecting your computer.
No I haven't bumped my head, Microsoft made a great, free program here.
Not only is it great and free, its un-obtrusive, and uses considerably less resources than other free (or even paid) anti-virus programs.

MSE is also updated daily, and offers a wide range of scanning options.
If you don't have much time, you can use the quick-scan to weed out the obvious issues. This tends to take about 10-20 minutes.
For a more thorough scan you can use the full scan option.
Additionally, when paired with Windows Defender in Windows 7, I've yet to run into any problems with my computer.