As anyone who works at an office building with badge or fob access controls know, most people tend to let anyone follow them in who wears an identification tag and looks respectable -- even if they don't know the person. A psychologist could do experiments as to why people do this, even in the face of persistent and often posted warnings to the contrary. 

A  sophisticated cadre of criminals is using the badge-swiping culture of Northern Virginia to steal from office buildings there, including some that house sensitive government facilities.

A series of thefts attributed to the group has triggered a joint investigation by the U.S. Secret Service, the Diplomatic Security Service and the Arlington County Police Department.

One of the buildings broken into included a State Department office that contained classified materials, although it is not clear whether the classified documents were the target.

According to a Defense Department memo, the thieves outfit themselves with laminated badges hung off lanyards. 

They loiter near building entrances that require card key or fob access and follow other employees in. "The thieves then enter unoccupied offices and steal property, especially cash and credit cards," the memo says.

There are at least 100 buildings in Northern Virginia that include sensitive government facilities. 

A Pentagon official called it a "major counter-intelligence problem."