LAS VEGAS - "Flash robs" are on the rise and convenience stores have been among the targets.

Like "flash mobs," flash robs involve a large group of people suddenly appearing - except their intent is to steal. They can be organized over the Internet, using social media like Twitter, or planned at some sort of large gathering. Last week, a flash rob targeted a store in Las Vegas; in February, a store in St. Paul, MN, was targeted. In Las Vegas, a group of 35 thieves swarmed to steal $600 of merchandise in minutes, plus the clerk??s cell phone. In St. Paul, more than 55 thieves poured into a store to steal merchandise.

These crimes aren??t limited to convenience stores. A flash rob struck a clothing store in Washington, DC, last week as well.

Security experts say that the best policy when facing a flash mob is to allow it to run its course. "The inclination might be to try to stop it. We don't want people to do that. We want store employees to be witnesses to shoplifting, not victims of assault," St. Paul Police Department spokesperson Andy Skoogman told KARE-TV.

Security cameras in all three incidents have helped identify some of the criminals. In Las Vegas, concerned bystanders also wrote down license plate numbers to help police apprehend the thieves

NACS contacted security experts to get further advice.

Dr. Rosemary Erickson, president of Athena Research, said that stores might also be on the lookout for big events - sporting events, concerts, etc. - that could spill into their stores, and to contact police at the first sign of potential trouble.

Both the Las Vegas and St. Paul events were captured on surveillance video.

"Unfortunately, security cameras aren??t likely to prevent or deter an incident, but they are helpful in identifying the suspects." Dr. Erickson said.