Sounds like you have mallware on your machine. Check out the following to
get rid of your problem.
Download/install/run Ad-Aware from:
http://www.lavasoftusa.com/
This will detect any spyware on your system. When you run Ad-Aware, click on
the ref update to get the latest up-to-date ref file, run Ad-Aware and
delete everything it finds.
You can also download/install/run:
Spybot - Search & Destroy from :
http://security.kolla.de/index.php?lang=en&page=download
Sometimes this will find problems that are not found in Ad Aware.
This program has two entries to it (Easy and Advanced). Unless you know what
you are doing, run it in Easy mode and also select Immunize after it is run.
Make sure you read the help on this first.
Hope this helps,
Martin