Be careful who you trust online. On Thursday, the federal police in Belgium disclosed that earlier this year, thieves used Facebook to set up a robbery that enabled them to steal the contents of a supermarket safe.

According to the related police report, in February, thieves "friended" the Carrefour supermarket's manager on Facebook, using the identity "Katrien Van Loo." One week later, Katrien invited the manager over for dinner.

When the manager showed up at the specified address that evening at 10:30, however, it turned out to be an empty building. Furthermore, two unidentified men overpowered the manager, gagged and blindfolded him, and stole his keys. While one of the robbers remained, the other searched the manager's apartment, where he found keys to the Carrefour supermarket. That robber's face was caught on the apartment building elevator's surveillance camera.

Later that night, said police, a third robber used the keys to access the store and steal the contents of its safe. Police didn't specify how much money had been stolen. That robber also was caught by surveillance cameras, but his or her face wasn't revealed.

Police have asked anyone with information about the case to come forward. They've also released surveillance footage of the two robbers and noted that, unusually, both appear to be left-handed.

One moral of the story is to ensure that virtual trust remains virtual--until proven otherwise. "Never admit unknown people to your circle of trust; you jeopardize your own safety and privacy as well as that of the friends who may be posting on your wall," said Rik Ferguson, director of security research and communications for Trend Micro, in a blog post that publicized the police report. "If you ever decide to meet a stranger, don't repeat this guy's mistakes. Do it first in a public place and do not go alone."

Ferguson also recommends conducting a quick background check on anyone who sends you a friend request, but who you don't recognize. "Do you have any friends in common? If you do not, this should raise a suspicion flag. If you can see any info on the person, do you have anything else such as schools or workplaces in common? Does the profile have a photo and if so is it one that you recognize? If you cannot see any info, mutual friends or photo, it's a definite no-no."

Of course, this isn't the first time that Facebook has been used as a robbery aid. Scores of news stories have reported on thieves trawling Facebook and Twitter for people's schedules and vacations, to better plan their robberies.

Last year, for example, WMUR Channel 9 News reported that police had arrested three suspects, and recovered up to $200,000 in stolen goods, as part of an investigation into 50 home burglaries in Nashua, N.H. Investigators said that the robbers used Facebook and other social networking tools to help ascertain when homeowners weren't going to be home.

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