Sorry for the stupid question, you never know.
If it were me, I would lock down the firewall to block ALL incoming traffic (unless it is mission critical), then reboot. If the problem stops happening, then you either made somebody's sh*t list, or one of your friends figured out your root password (or escalated their user account, which isn't to hard to do).
I doubt any serious hackers out there would be interested into cracking your box so they can annoy you by running top. They are to busy being 1337