My father has had similar problems just recently. There is some good free software for removing this stuff from your computer such as Ad-Aware, Bazooka, 'Spybot - Search & Destroy', SpywareBlaster and many more. I found that I had to use about four spyware removal programs in order to correct the problem!It's the second day that I have been subjected to professional hacking attempts. Someone keeps trying to turn my computer to a zombie for sending Spam. This Someone is also intrested in the information I have saved on my computer. I'm on watch!
Just go to http://www.download.com and you will find that there is a section entirely devoted to spyware.
The most common causes of infection currently appear to be security holes in Microsoft Outlook and Internet Explorer (IE). So I recommend that you go to http://www.mozilla.org and download Firefox which is a far more secure internet browser than IE and in my opinion a great improvement on IE. Whilst your at it you may wish to download another email program such as Thunderbird.