While it is difficult to physically assault someone over the network, it is entirely possible to threaten, harass, abuse, frighten, etc., someone. There has been at least one case of Rochester Police being called in and assault charges filed in response to threats and harassment via email, talk, and so on. Stalking on a computer is often a prelude to more intrusive stalking and harassing. Local cases have included hacking of an individuals phone mail mailbox, written notes stuffed under a dorm room door, and physical assaults.
Harassment, especially sexual or racial harassment, is a violation of UR policy. It is unclear to us (we are not lawyers) where the line between free speech and harassment is drawn. If any problem arises regarding harassment, the UCC (University Computing Center) staff are required to lock the harasser's account (if a local account) and move the issue up to the Dean's Office for resolution. We will follow similar guidelines, although we may have an intermediate stop at the Committee for School Computing (CSC) first.
We may also be required to provide evidence to a law enforcement agency.
As an aside, it is illegal to threaten the President of the U.S. in any way. Doing so in a posting to a newsgroup, or in a WWW home page, or by sending email to the President, will surely get you (and the systems staff) a visit from the Secret Service. It will not be pleasant, and may get you a very long term in a federal prison. Do not even think of doing this as a joke (the Secret Service cannot have a sense of humor regarding this issue).