Free Anti-virus programs. April 2014. Windows XP and Windows 7

Here's my summary of the anti-virus programs I have experimented with.

AVG free anti-virus
http://www.avgfree.com.au/

Avira  Free anti-virus
http://www.avira.com/en/avira-free-antivirus

BitDefender anti-virus
http://www.bitdefender.com.au/solutions/free.html

Malwarebytes
http://www.malwarebytes.org/downloads/

Microsoft Security Essentials
http://windows.microsoft.com/en-gb/windows/security-essentials-download#dlbutton

Also refer to..
FileHippo for anti-virus software
http://www.filehippo.com/search?q=anti+virus

And read here for unbiased reviews and tests...
AV-Comparitives
http://www.av-comparatives.org/

All free and all do the job. Pick one.
** Disclaimer - all these sites will try to make you buy the paid version, of course, so be careful which button you click on. Even then, you will receive regular messages to upgrade. Stick with the free version if you can. Buy the full version of you like how it works, I usually do after a trial.

Cheers. Si.
Checked April 2014 for link and relevance. Still valid for Windows XP and Windows 7