Actually, I think there's a pretty good way that's already built into windows. Basically, look at file modification dates and times. Go into Windows Explorer, do a file search based on time -- like files modified in the last day or so -- and then sort the column by file date. You will see a bunch of files at the top of the column that got modified when you booted up, and any activity since. Going back in time (down the column), you can see when files were modified before that. It's not as straight forward as a logging program, but you'ld be surprised at what you can find out using this method. And if any files have time/dates for a period when you were, say, not at home (or work), then I would begin to suspect that someone else has been using the computer.