You should get spybot search and destroy.
http://www.safer-networking.org/en/download/index.html
Spybot search and destroy is the best anti-spyware because of three important features that the other "FREE" software do not have.
1) Immune feature - Spybot search and destroy immunize your computer against spyware by modifying
Internet Explorer to block a lot of the bad stuff known to Spybot.
It also prevent spywares/adwares/trojans from coming back again.
Other anti-spywares program can remove the spywares but cannot prevent it from coming back again and again.
2) Registry monitor - advance feature TeaTimer module can monitor
and deny changes to registry by all malwares.
Windows registry is a database use by Windows Operating System.
Usually, no program are suppose to change the registry except
when you install a new software or hardware drivers.
3) Hosts file locking - advance feature that prevent web pages hijackers.
I like spybot because I found that it is a better strategy than other anti-malwares.
Instead of trying to keep the virus/trojan/spyware/adware signatures up-to-date
( impossible task because new one keep appearing )
Spybot try to stop UNKNOWN malwares from infecting your system by using
tea timer to deny unauthorise changes to registry.
This help to prevent malwares from installing on your system behind your back.
Therefore, it is better than other anti-malware program that do not offer the same
protection to windows registry.
see comparison
http://www.2-spyware.com/compare2.php