WASHINGTON - A top homeland security lawmaker has called for an investigation into possible cyber attacks on computer systems at the Homeland Security Department.

Rep. Bennie Thompson, D-Miss., said he believes Unisys Corp -- the company that holds the $1.7 billion contract to build parts of the Homeland Security Department's computer network -- is at fault for these network break-ins. Thompson chairs the House Homeland Security committee and asked the department's inspector general to investigate.

Thompson's investigation found that dozens of computers may have been compromised by hackers, but the incidents were not noticed until months after the attacks. Information taken from the department's systems was sent to a Web service that connects to Chinese Internet sites, and contractors gave misleading information to the department about the attacks, according to Thompson's findings.

"The department is the victim not only of cyber attacks initiated by foreign entities, but of incompetent and possibly illegal activity by the contractor charged with maintaining security on its networks," Thompson wrote in a Sept. 21 letter to the department's inspector general.

Homeland Security spokesman Russ Knocke would not comment on Thompson's allegations. But he said the Unisys contract is being subjected to a new round of competition that includes other contractors. While Unisys is not prohibited from competing, past performance will be considered in the contract award, he said. Unisys was awarded a one-year contract in 2006 with two one-year options.

"We are aware of, and have responded to, malicious cyber activity directed at the U.S. government over the past few years," Knocke said. "We take cyber security very seriously."

The FBI would not say whether it is investigating Unisys.

Unisys disputed the committee's findings, but company spokeswoman Lisa Meyer would not go into detail because of security concerns. The department's inspector general will decide in the next few days whether to pursue the investigation, a spokeswoman said Monday.