FBI investigators are working on a computer intrusion case at the Crystal Lake School District in Crystal Lake, Illinois, said Ross Rice, a spokesman with the FBI's Chicago office. But several other school districts also believe that they have been hit by the same malicious software, Rice said.

The FBI believes that the Clampi virus, already associated with a rash of banking thefts throughout the U.S., may be to blame, Rice said.

Rice declined to provide more information on the case because it is still under investigation, but say that as much as US$350,000 may have been taken from the Crystal Lake District alone. The district's superintendent, Donn Mendoza, did not return a call seeking comment for this story.

Three Illinois school districts are thought to have been hit over the summer, but other school boards nationwide have been targeted by the scam.

Designed to steal banking credentials from its victims, has been an increasingly thorny problem for small businesses and government agencies in the U.S. Investigators say organized criminal gangs based in eastern Europe are moving millions of dollars per day out of the U.S., using Clampi to access bank accounts and then transferring money to unwitting who then transfer the money offshore.