Is it possible for someone to hack into a computer while it is hooked up to an unsecured network and as a result for the browsing history to show websites that were accessed by the hacker, but not the actual computer owner? If someone was pirating your wireless signal you wouldn’t be able to view what they’d browsed without seeing their computer directly or accessing the settings for your router.

It is however possible for older web-browsers to be forced to save websites as favourites without the user being aware. This occurs visiting a macious website containing SCRIPT which might save one or more websites and normally also attempt to change your homepage.

If it's browser history, I would suggest checking you don't have kids or someone using it in the middle of the night, etc. The other way might be REMOTE connection to your PC, in which you would be able to see someone moving the mouse, typing, etc, remotely. If you don't USE these services, disable them as they are just a security hole, if you do use remote access sometimes ensure its a strong password and/or IP ADDRESS fixed.