I KNOW this forums is about BT... but it's also filled with people who know a lot more about security then I do, and frankly, I didn't know where else to turn. Besides, this IS pentesting, right?
Here's the full story:
I was playing around with Ettercap in Backtrack, trying to get it to capture user/pass info from my other computer (Windows XP), when I discovered that the firewall on that computer was smart enough to 'protect' against spoofing. So I turned if off, to see what would happen. Indeed, Ettercap then worked.
However, soon after that, the PC suddenly, without any warning whatsoever, rebooted (only 'notable' thing about it was a very slight noise coming from the speakers).
I checked again: every time I'd turn the firewall off, the computer would reboot a short moment later. I've turned DMZ off on my router (it was forwarding everything to my PC), and the problem stopped. EDIT: After more tests, it seems that it happens even with the DMZ turned off.
Then I turned DMZ on for my laptop (dual boot Windows XP and BackTrack3), and turned the firewall off there, and this time, nothing happened; laptop kept on running.
So, something must be wrong with my PC. Now, since any changes to the DMZ cause my router to reboot, and since I have a dynamic IP, I doubt that I am 'the' target of some attack... more likely (if this IS an attack), it's set against a whole range of addresses. But the thing I want to know: is this some kind of vulnerability, or just some system screw-up which causes it to reboot (unintentionally)? And, most importantly, how can I try to pinpoint the problem (or better yet, fix it)?
I should also note that I keep my system up to date with all the updates, and I already checked antivirus.
PS. Of course the obvious thing is NOT to turn the firewall for the time being, but that still leaves something wrong with the system itself.