Would you consider
Avast too? It's a good free tool.
You haven't been visiting
naughty sites have you?
They have a habit of installing pop-ups, (and diallers in the olden days) or setting your web-pages to be always opened through their site and then they can pop-up some more. I got hit by going to a mis-typed address once. It took me ages to get clean again.
If you do go with Avast, run a full scan and a deep level boot scan. Leave it running overnight. It's not quick, but it is good. As a one off, you can also use AVG, but that requires registration after a short period and then wants you to pay too. You can always uninstall it after a full scan.
Anway, isn't this a Unix forum? Ho hum, we all have to live with Windoze, so let us take away as much pain as possible. Any other suggestions?
Robin