I don't want to scare you, but if my computer would do such strange things, my first bet would be a virus.......programs are not supposed to act like this, unless they are told to do so; either by configuration or by some nasty controlling it.
Check your system using any of these programs (I reckon using all of them):
http://www.lavasoftusa.com/software/adaware/(free) http://www.grisoft.com(good free AVG) http://www.ewido.com(free trial which can still be used and updated after the period has ended -the best in my opinion) http://www.ccleaner.com/download/(free) Spybot - Search & Destroy (FREE)
If you can't get rid of it go here and get some free computer help:
http://norbiesworld.co.uk/computerhelp 