Several government agencies within the Department of Homeland Security admit they are regularly victims of computer break-ins at home and overseas by hackers finding their way into the department's cyber network.

More than 800 security incidents plagued the department over the past two years, including viruses, password-stealing programs and "Trojans" or hacker tunnels found on some workstations. Problems have cropped up at FEMA, the Transportation Security Agency, the Coast Guard and other agencies.

The House Subcommittee on Emerging Threats, Cybersecurity, Science and Technology asked officials Wednesday how they are improving their cybersecurity to prevent such incidents from happening again. Chairman Jim Langevin, D-R.I., called the reports "very disturbing."

Some security problems include unauthorized software installed on department computers, misconfigured firewalls and unauthorized disclosures of classified data.

It's not just happening within the Department of Homeland Security. The Department of Commerce was hacked last year by computer criminals in China that forced one to get rid of hundreds of computers and set up a new network system.

Similar attacks at DHS show that someone on the outside likely has access to department accounts.

Homeland Security Secretary Michael Chertoff backed information technology efforts at the department.

"I don't think there's a particular vulnerability at DHS," Chertoff said.

Scott Charbo, chief information officer for DHS, has done a "good job of consistently raising the level of security," Chertoff added.

The department received a "D" on its annual cybersecurity report card from the Federal Information Security Management Act. NASA received a "D-minus" and the Defense Department got an "F."

FOX News' Caroline Shively contributed to this report.