With my incredible artistic and investigative talents, I have decided to make a tutorial to help with this sort of issue. It's complex, but with the aid of Paint, a red pencil tool, and annoying embedded 2 megabyte .png files I know we can get through this.
Step 1. Click the circled button.
Step 2: click the circled button.
Step 3: add the circled text to the URL
Step 4: note the new IP logging on and the old IP failing to log back on.
Conclusion: Shazam, you have now found your hacker's IP and can report the problem to an admin instead of whining about it to the public at large.