|There are many different anti-spyware programs out there, and anti-virus.|
I like Panda Cloud Antivirus, it's small free and powerful, it runs live virus definitions off the web.
SuperAntiSpyware and Spybot - search and destroy are fairly good too.
Back up all your important files immediately!
There are always more drastic measures available if it's impossible to fix..
Also check add/remove programs to see if you've accidentally installed any kind of weird toolbar or program recently. These can be stubborn to remove.