I would honestly need more information to give an accurate and thorough remedy.
1) your operating system
2) Number of users on the computer
3) Exact name of the product being presented or name of virus/adware if you know it.
4) when you began to notice the problem
For a more general solution, I would start by scanning your computer with spybot. That's my personal favorite. You can find it
here.
The problem is that this won't get rid of your problem, if this is the situation I think it may be. Now, I wouldn't normally advise this, and people can scream if they really want, but if you're running windows XP or Vista or Mac OS X 10.5 you can either use System Restore or Time Machine, respectively, to "backtrack" your computer to a few days before you contracted this "issue."
Two problems, this doesn't always work, though it ususally will, and if you have to go with removal, you'll have to do it manually.
In order to remove spyware and viruses ( I still like "viri") manually you'll have to isolate the specific processes running in relation to them and physically erase them. I would recommend
Eraser.
Hope this helps. More information could mean a better solution. BTW, if you want to try the restore point, type restore point wizard in windows help. One more word of caution, by loading a restore point, you will effectively be removing all install information done after the date the restore point was created. This can be a serious issue if you don't know what you're doing.
Hunter.
EDIT: Good call on that ZeroG, forgot to cover that part.