The security of industrial systems like this has come under scrutiny in the past year following the release of the Stuxnet computer worm, which is thought to have sabotaged systems used by Iran's nuclear program.

In this case, though, the hacker says he's a disgruntled insider. Insiders seeking revenge are responsible for about 10 percent to 15 percent of all industrial security computer incidents, said John Cusimano, director at the Security Incidents Organization. His company maintains a documenting failures of computer systems used by SCADA systems.

"It's probably still up in the air as to whether this was a real threat or a hoax," Cusimano said.

The IDG News Service