This happened to me twice in college, minus the expulsion part. In the less interesting case the University sent around a form to be used in nominating student speakers for commencement. It included a drop down that was keyed off of student id. Student ids were regarded as private.
The school required everyone to either buy health insurance from them, or provide proof of insurance. They had a webapp where you could report this data. The login required your student id, name, and birth date (thanks Facebook). If you visited the app after using it, the form auto-populated with your health insurance information. I brought it to the attention of the University and they took down their nomination app in a matter of minutes.
In the more exciting incident, someone at Sungard called my university and asked them to have the campus police arrest me. (Edit: Quite boring, really http://seclists.org/bugtraq/2008/Jan/409)