How do I find out what was taken and how?
how do I insure this doesn't happen again?

An outside source has just download my hard drive, I caught this midway through, and reset my computer. My fire wall did not stop this, or even notify me. I found out when trying to open files and was told that they were already in use by another user. I know my documents folder and a couple of others were accessed and being copied. I don't know exactly what was got. I have been developing a video game, some of those documents may have been among those copied. several have already been copyrighted, but many are new or updated. I am printing them now to send registered mail. that will cover me until I get the new copyrights.

How do I find out what was taken and how?
how do I insure this doesn't happen again?