The FBI has revealed details of an investigation into pirated Cisco hardware bought by the US government.

Operation Cisco Raider was launched after government departments complained that they had been sold networking hardware that, while branded Cisco, was built by third parties.

The investigation found that over 3,500 pirated items had been sold to the government at a value of $3.5m.

"Counterfeit network hardware entering the marketplace raises significant public safety concerns and must be stopped," said Assistant Attorney General Alice S. Fisher.

"It is critically important that network administrators in the private sector and government perform due diligence in order to prevent counterfeit hardware from being installed on their networks."

Operation Cisco Raider led to 10 convictions and $1.7m in fines, and was declared a success.

However, a PowerPoint presentation was leaked at a briefing yesterday which appeared to suggest that the investigators also had security concerns.

The briefing said that Trojans and other malware could have been embedded in the counterfeit routers that could be used to bring down critical parts of the national infrastructure.

"This unclassified briefing was never intended for broad distribution or posting to the internet," said James Finch, assistant director of the FBI's Cyber Division.