Bomb Threats on Campus

ABC News' The Blotter reports a disquieting trend to begin the academic year:

At least 13 U.S. universities, including Princeton, MIT and Carnegie Mellon, have been targeted for anonymous e-mail bomb threats as students return to classes, federal and local law enforcement authorities tell the Blotter on ABCNews.com.

One of the schools, Clemson University, in Clemson, S.C., was targeted again today and an evacuation was ordered, ABC News has learned.

"We have had three in the last 10 days," Clemson University spokeswoman Robin Denny said of the bomb threats. She said the university has been sending out e-mail alerts to students, faculty and other personnel, saying evacuations were in progress after each threat.

The FBI, regional authorities and university police are investigating the spate of threats that include a set of difficult-to-track threats that use Internet remailer services to eliminate the sender address and render the threat anonymous and more difficult to trace, the FBI confirmed.

"The FBI is aware of the spate of bomb threats," FBI spokesman Richard Kolko told ABCNews.com. "Working with university police and our field offices, we are investigating."

The threats, timed to the resumption of classes at schools around the nation, may simply be the work of pranksters, but officials are taking no chances.