Help! I think my laptop/ wireless connection is being hacked?

I had a virus removed from my computer last year by a local IT firm. They also rebuilt the computer and installed a version of Vista on to it. I now suspect they have have access to my laptop (browsing history etc) either through the router or the software they installed on the computer. Is there any way of checking to see if this is the case or making changes/ removing and reloading software etc to rectify this and give me peace of mind?