Fear mole-men with bombs. That, more or less, is the message from Manhole Barrier Security Systems, which on Monday warned that cities need to do more to protect against assaults on infrastructure launched by underground attackers.

More, in this case, consists of buying the company's patented locking manhole covers.

Mike Manoussos, the company's chairman and CEO, argues that it's too easy for terrorists and vandals to enter the subterranean world, where telecommunications and utility lines are buried.

Interestingly, that's a view shared by those not selling locking manholes. Irwin Pikus, a former commissioner of the U.S. President's Commission on Critical Infrastructure Protection, wrote a report titled "Manhole Security: Protecting America's Critical Underground Infrastructure." In it, he warns, "Without manhole security, the United States risks suffering significant consequences resulting from an attack on underground infrastructure, including incalculable economic damages, large numbers of civilian casualties, and considerable disruptions to our urban way of life."

The trouble is that Manhole Barrier Security Systems doesn't have an incident to cite that demonstrates how manholes have actually been exploited to cause harm. The company mentions the Feb. 26, 1993, blast in the parking garage of the World Trade Center, which though underground, has more to do with cars and bombs than manholes.

The company also points to how theft of manhole covers by the homeless in Philadelphia led to the injury of a graduate student and a multimillion dollar settlement. It's a sad case, to be sure, but one more of interest to municipal attorneys than to those responsible for security.

While there are certainly places where manhole covers should be locked, like prisons, the idea that replacing a heavy object with a locked one will deter a determined attacker vastly oversimplifies how physical security can be implemented. Imagine how much easier computer security would be if all one needed was a firewall.