UPDATED 05/11/11 7:08 p.m.

CHICAGO (CBS) — A warning to those who come downtown: Chicago Police are on alert for a new brand of criminal.

Sources say in the past three weeks, there have been more than 35 arrests for wilding and flash mob attacks.

CBS 2’s Suzanne LeMignot reports, Chicago police are stepping up patrols to try to put a stop to it. Recently there was a large police presence in front of McDonald’s at State and Chicago and officers on horseback at North Avenue Beach.

The increased patrols have been noticeable among residents.

“I saw cars, [officers] on horseback and just walking around,” said Joseph Golz, who was cycling along the lakefront. “They were present, now I know why.”

Sources say the lakefront has been targeted by large groups of teens, carrying out wilding incidents. Two people riding bikes on the path at North Avenue Beach were recently surrounded by about 100 teens.

Both were knocked off their bikes, then thrown into Lake Michigan.

“I think it’s terrible,” said Jill Gomberg. “I think it’s really scary. The lakefront is like a sanctuary.”

Sources say flash mobs have also entered the McDonald’s at Chicago and State. About 70 teens stormed into the place a few weekends ago. A source says the eatery was closed down for three hours after the incident.

“When you talk about flash mobs, I think it all boils down to one thing, parenting,” said Police Supt. Terry Hillard. “People are not taking control of their kids. It all starts at home.”

The North Face, Filene’s Basement and Express along Michigan Avenue have also been the target of flash theft mobs recently. Teens enter a store, steal as much as they can in seconds, and leave.

“I actually saw an officer chase down a young girl once at the corner of Huron and Rush,” said Miralem Mahmutovic, who witnessed the incident. “She ran out of Express.”

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