3 suggestions for you:
Run malwarebyes (google it) its one of the better malware removing programs. Just download it and install/run it.
May I ask which torrent program you use? Sometimes when you install those, it installs this 'feature' along with it. Under control panel, go to add/remove programs (if using XP) or programs and features (if using win7) and look through the list and uninstall anything you don't recognise
Which web browser do you use? If it's Internet Explorer, check the addons list. Where this is varies a little bit by version, but give this a try. Go to Options then Programs tab, then Manage Addons button. If you see stuff in there you don't recognise right click and disable them.
Give that stuff a go then report back and we can proceed accordingly