A 21-year old Indiana resident was slapped with a 21-month jail sentence for his role in a hacking attack that compromised computers at the Department of Defense, law enforcement officials recently revealed.

The attack was launched by international hacking gang Thr34t Krew (TK) and took place between October 2002 and March 2003, according to a statement from U.S. Attorney for the Eastern District of Virginia Paul McNulty.

Former TK member Raymond Paul Steigerwalt was sentenced Friday for one count of conspiracy to commit fraud and related activity in connection with computers and one count of possession of child pornography, officials said. He was also ordered to pay restitution to the Defense Department of $12,000.

Steigerwalt and his gang were accused of creating a worm that infected Internet-connected computers. The worm installed a trojan software program, allowing them to control the infected machines. At least two computers at the Defense Department were infected, McNulty's office said. It was not clear what damage was done.

Steigerwalt's sentencing came as a result of an investigation involving the Defense Department, the FBI, the U.S. Army Criminal Investigation Command, the U.S. Secret Service, the Air Force Office of Special Investigations, the Riverside California County Sheriff's Office and the National Aeronautics and Space Administration.

Two other men in North East England were held in 2003 for their part in creating the TK trojan. At the time, the U.K.'s National Hi-Tech Crime Unit said that the virus had infected approximately 18,000 computers around the world, causing an estimated £5.5 million ($10.3 million) in damages.

The sentencing of Steigerwalt last week represents a small victory for law enforcement officials, but the incident could still prove somewhat embarrassing for the Defense Department, according to Graham Cluley, senior technology consultant at Sophos.

"Most of these government agencies are pretty clued in on security threats but the problem is that they only need to be unlucky once to have egg on their face," Cluley said.

International hacking groups, like Thr34t Krew, appear to be on the rise and they are increasingly focusing on money making schemes, Cluley said.

Security experts are warning organizations to be aware of sophisticated attacks designed to steal information or perform extortion, by threatening to launch a denial-of-service attack against a Web site unless money is paid, for instance.