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While there are not too many details to go on, NBC4 is reporting that the U.S. Department of Homeland Security has warned Metro of a threat to its transit system. That’s according to an internal memo NBC4 has seen: “Someone traveled to Turkey last July to obtain a U.S. visa to come to the States to blow up an unspecified Metro station.”

It’s a low credibility threat. (And besides, Metro doesn’t need terrorists to injure or kill you; it’s pretty good at crashing subways or letting you get caught up in a 70-person brawl.) So remember: Keep calm and carry on!

Photo by Flickr user acrib via Attribution-No Derivs Creative Commons License