At least 57 Petaluma area residents have had thousands of dollars siphoned from their bank accounts after using self-checkout lines at the Lucky Supermarket on Lakeville Highway, according to police.

A trickle of reports over the weekend turned into a deluge Monday morning, with more than 40 people filing police reports throughout the day.

Despite initial denials by Lucky's corporate owner that the Petaluma store had been targeted by thieves, police said they had little doubt about where the account information had been stolen.

"We're being really specific to ask &‘Where have you been using that card?' and Lucky is the common denominator," Sgt. Steve Nelson said.

The average loss appears to be about $500, often happening in $300 and $200 increments to get around ATM withdrawal limits, Nelson said.

The thefts have occurred all over the region, including San Francisco, Santa Barbara, Northridge and Reno, Nelson said. That tells him that a very organized, sophisticated group is behind the scam.

A spokeswoman for Modesto-based Save Mart Supermarkets initially said Monday the Petaluma store was not one of the 20 locations where "skimming" devices had been found hidden in ATM/credit card readers on self-checkout lines in November.

But late in the day, spokeswoman Alicia Rockwell acknowledged that stores in Petaluma, Novato and Sunnyvale had also been hit, pushing the total to 23. She said a "breakdown in communication" had occurred between company officials and the technicians who combed all 68 Lucky stores in Northern California after the first devices were found Nov. 11.

"Obviously, this is changing by the minute," Rockwell said.

The company's Nov. 23 alert assured shoppers the breach had occurred at only 20 of its stores and said the grocery chain was unaware of "any reports that customer accounts were compromised."

That changed late last week, when the company started getting reports that employee and customers' bank accounts had been compromised. On Monday, the company confirmed that 80 employees and customers so far were victims of thefts or attempted thefts from their accounts. Most occurred over the weekend, Rockwell said.

She said the company's loss prevention department is working closely with banks, card processors, local law enforcement and even the FBI to figure out who is responsible.

The company urged shoppers who used the self-checkout lines at the affected stores in October or November to cancel their accounts and talk to their financial institutions about how to protect their money. The company said it has no idea how long the skimming devices were actively gathering customer information.

"We're concerned enough at this point that we really think people should err on the side of caution," Rockwell said. "It's your checking account compared to your credit card, so that's a huge impact."

Petaluma resident Kevin Cotter says he's "a little ticked off at Lucky" after learning his account was drained of $800 over the weekend.

"They make sure to lock up their cash registers, but when it comes to their credit card machines they don't really seem to care," said Cotter, 45.

Cotter, who works at an information technology startup, said he got a call Sunday night from his bank alerting him of possible fraudulent activity on his Summit State Bank checking account. He logged in and saw four transactions totaling $800 in withdrawals from Gilroy and Santa Maria.

"They basically cleaned out that account," Cotter said.

Even though his bank has assured him he'll get his money back, Cotter is upset because the company knew there was a massive security breach but never alerted Petaluma customers to be on the lookout.

"There was no note by the register that said &‘Hey, be careful, this might have happened,'" Cotter said.

Willits resident James Johnson said he and his wife are about to close a deal to buy their first home on Wednesday and worries that the $1,369 in fraudulent charges they discovered over the weekend would derail the closing. The charges were made at Nordstrom in Newport Beach, he said.

Since they only started shopping at the Lucky in Ukiah two weeks ago, he immediately assumed the local store had been hit, as well. But later he thought harder about it and realized that his wife popped into a Lucky in San Jose last month.

"I bet that may have been where our information was stolen," he said.