NEW YORK, May 9 (UPI) -- The possibility of bogus computer products in U.S. computer systems has become an increasingly daunting concern for the FBI and Pentagon, officials say.

Concerns have been influenced by Operation Cisco Raider, which resulted in 15 criminal cases centered on counterfeit products partially purchased by U.S. military agencies, contractors and electric power companies, The New York Times (NYSE:NYT) reported Friday.

During the 2-year investigation officials acted on 36 search warrants, which led them to find 3,500 bogus Cisco network products valued at around $3.5 million, the FBI said.

The danger of the situation is in the possible remote hacking of secure computer networks, FBI officials said in a January briefing at the Office of Management and Budget.

"We did not find any evidence of re-engineering in the manner that was described in the FBI presentation," Cisco spokesman John Noh said.

Some industry technologists say they believe the threat of counterfeit computer components is strong.

"There are enormous vulnerabilities in our defense and national security infrastructure," said Peter Levin, chief executive of DAFCA Inc., a company that works to stop computer chip tampering.