You could add some baselining software to your system next time such as Redhand www.redhand.com this comes in two versions single user and network user. So that you can audit your machine before and after. Or you could run a file search for anything that has been altered after the date you sent the machine for repair. Removing the hard drive could possible invalidate the warrentee so is unadvisable. And encrypt the system and pw protect what you want hidden. Hope this helps.

Damien Harrison