Doubler
If you don't use firewall, I suspect someone has managed to put spyware (is that the right word?) on your machine.
Have you tried using Spybot (admins - please remove link if not appropriate)?
It scans your machine and then tells you any problems it finds, then you can remove that problem.
Best of all, it's FREE!
I hope this solves your problem.
k:
http://www.download.com/Spybot-Search-Dest...4-10122137.html