Its appears your not running an antivirus program, why is that ?
Install atleast a free av program, update the program, since it's being ran for the first time do a full system scan preferably while the pc is in safe mode.
There are several to choose from mentioned here
http://forums.spybot.info/showthread.php?t=279
Put in place a good hosts file
http://www.mvps.org/winhelp2002/hosts.htm
How To Download and Extract the HOSTS file:
http://www.mvps.org/winhelp2002/hosts2.htm
Repeat that proccess about once or twice a month