And next tonight, a heads up from police, just three weeks before the holiday shopping season begins. They are tracking a new type of crime, popping up across the country. It's called flash rob, a play on the term flash mob, instead of a fun loving dance it has a vandalizing twist. Here's abc senior justice correspondent pierre thomas. Reporter: These five men walking into a chicago area sports authority are about to commit the most brazen theft you may ever see. There they are running out of the store, rolling racks full of clothing, take another look. They are stealing racks of coats, it's over in less than 30 seconds. They're not done. The same thieves are believed to have targeted two other sports authority stores, this week alone. Police are seeing crimes like this around the country. So called flash robs. Coordinated groups of thieves, who swarm stores. The chicago area clothing store was hit last year. We had about 15 or 16 kids in the store before I lock the door. Overwhelming sensation of just not able to do anything about it. Reporter: In some cases the theft is loud and crazy, like at this florida walmart. In others, it's stunningly calm. Authorities believe the trend began with teenagers stealing candy and drinks like you see here. There's now also concern that organized criminals are adopting the same tactics, making off with thousands of dollars in merchandise. It's all part of a massive problem of retail theft. U.S. Stores may be losing up to $30 billion a year to shoplifting. The fear this holiday season, that the wrong kind of mob might show up at the nation's stores. Pierre thomas, abc news, washington.