Just one question you did say this is your computer not belonging to the college? You may need to contact the system admin from the college and see if he/she even knows about the problem. Chances are that they do know about it. If it is a college computer then could secure it for you or at least start tracking who and how this is being done.

Now if this is your personal computer then:

You are going to have to secure your computer a lot better than it is right now. I would start with a firewall and antivirus. You can find these in the download section on the right hand side of the Antionline homepage. I would suggest Zonealarms or Tiny for firewall and which ever antivirus you like I like panda myself.

One thing you may think about is that it could be a virus not just some guy on the network. Especially since it has happened to multiple people. Just food for thought.

Hope this helps.