Sources said FBI agents are also looking into the possibility that Ptech executives may be involved in a charitable organization that sends money to the Middle East and whether that organization's funds might be diverted to al Qaeda. One federal source said the FBI has no evidence this happened.

It was not clear if that organization was the Muwafaq Foundation -- which U.S. officials have said was an al Qaeda front -- or another Islamic charity.

U.S. Customs agents raided Ptech's headquarters at midnight and downloaded information from company computers for further investigation, the sources said.

Officials are especially concerned that several of Ptech's customers are government agencies, including the Department of Energy, the FBI, the U.S. Air Force, the U.S. Postal Service, the Naval Air Systems Command, the Federal Aviation Administration, the House of Representatives and NATO.

One government official said "absolutely no evidence" exists that the company's product had been tampered with but the investigation was under way.

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