Special spying software has ported to the Mac.
Rampell Software's Spector for Mac is designed to track a Mac activity, allowing users to know if their Mac has been used for anything unauthorized in their absence.
The software records Web sites and chat rooms visited, programs used, and keystrokes typed. Spector also takes occasional screenshots. It is password-protected and virtually undetectable, launched via a hot key.
Spector is compatible with Mac OSs 8.0-9.2, although Rampell plans to release an OS X version "soon". It costs $69.95 and distributed by SpectorSoft.