Stores across the Delaware Valley are packed with shoppers this Black Friday. Many retailers have more than paying customers on their minds, and the new shoplifting threat they’re dreading has already hit the Philadelphia area. “Flash mobs”–those gatherings of people based on social media or text messaging who dance or sing in the mall food court–have a new less-wholesome cousin.”We’re seeing what we call ‘criminal flash mobs,’ people that get together for the purpose of stealing from stores, scare employees, scare customers, cause damage to our locations,” said Joseph LaRocca, with the National Retail Federation. His group is advising members on how to deal with the mobs. In the Philadelphia area in June, a mob hit a Sears store. Upper Darby, Pa. Police Superintendent Michael Chitwood says he’s glad no one was hurt. “We received a radio call about a group of males that came into the Sears…in excess of 20,” said Chitwood. “They took wrist watches, underwear, various other items and then they were in and out in a matter of minutes. They ran out the door and…police arrived, they arrested approximately 15 males.”Joseph LaRocca says retailers are increasingly worried.”In July we polled retailers across the country and about one in ten companies have experienced a criminal flash mob incident in their stores,” said LaRocca. “About 50%, or half the offenders were apprehended and in most cases these were juvenile offenders.”LaRocca says the incidents happen so quickly, there’s little time for store employees to react. “We have asked companies to monitor the Internet, work closely with mall security and law enforcement officials to identify where a possible criminal flash mob could be headed,” he said.LaRocca says once a group starts stealing merchandise, workers should stand back, take note of what they’re stealing, save any video and then work closely with law enforcement to track them down.Police Superintendent Michael Chitwood also advises employees not interfere.”Retailers have to call the police right away and not try to stop these individuals who are in there in these groups–let them take the merchandise, merchandise can be replaced,” said Chitwood.University of Florida research scientist Dr. Read Hayes is the director of the Loss Prevention Research Council. He says the so-called “flash robs” are still rare but it’s difficult for stores to prevent them.”Some of the larger chains–two or three at least–are now starting to look at monitoring social media to look for patterns or possible indications, what we call pre-indicators,” said Hayes.Hayes says there are steps stores can take to prevent the loss of merchandise if something does happen.”If you have apparel, you can criss-cross the hangers. That way you can’t just grab them and pull them off, and try not to locate some of the high value low profit-margin items too close and not in clusters so they’re readily removeable,” said Hayes.But Hayes says there’s not much convenience stores can do because the group that hits a 7/11 is looking less for high value merchandise and more for stories to tell later. He says cameras may help deter criminals and catch them if something does happen.