Recent news stories highlight what experts say could be a growing problem: disgruntled IT staffers using their knowledge and skills to cause expensive problems for their employers.

Terry Childs, an IT staffer for the city of San Francisco, made headlines in July when he blocked access to critical parts of the city’s network and refused to turn over the password.

He was arrested, held on $5 million bail and eventually turned the passwords over while in prison.

In another recent case, former IT manager Steven Barnes was sentenced to a year in jail after he hijacked his ex-employer’s e-mail system.

Barnes was fired by Blue Falcon Networks, and took revenge by hacking into the company’s mail server and using it to send spam containing viruses and pornography.

Problems could be even more widespread than many companies realize. More than 88% of IT staff said they’d take sensitive company data with them if they were fired, according to a recent survey by security firm Cyber-Ark.

Can insider hacking be prevented?

Experts warn that insider IT sabotage could become more common. As the economy continues to sink, more tech workers are laid off and overall job security and satisfaction decreases.

But experts also say many problems can be avoided. HR and IT management both have a role to play in preventing attacks like those listed above.

The first line of defense: a thorough background check for all IT workers.

After the Childs case, San Francisco officials admitted its criminal background check only looked at records in California. But Childs had a list of convictions from other places, including four years spent in the Kansas state prison.

Of all the cases of insider sabotage, 30% involve an employee with a criminal history, according to a study by the Computer Emergency Response Team at Carnegie Mellon University.

IT managers should also be on the lookout for the warning signs of potential security threats. The signs could include staffers suddenly working long hours for no apparent reason, asking for access to information unrelated to their jobs, and printing or e-mailing large amounts of data.

And since many incidents happen when staffers are angry about losing their jobs, IT should be sure passwords are changed when an employee exits.

Tags: e-mail, ex-employee, IT staff, sabotage, Terry Childs