ATM users beware — cash machines can harbor an illegal credit- or bank-card copying device, known as a "skimmer."
The Peninsula is experiencing a jump in skimming cases, which started around March 13, Los Altos Police Sgt. Matt Hartley announced.
But the instances were not made public by police until Monday.
On March 15, a man using an ATM at California Avenue's Wells Fargo bank branch in Palo Alto spotted a skimmer on the bank-card slot, Palo Alto police Det. Kara Salazar said Monday.
Los Altos police have also recently recovered skimming devices on ATMs at the ARCO gas station at San Antonio Road and Loucks Avenue and at the Bank of America at South San Antonio Road and Hawthorne Avenue, Hartley said.
The number of cases "suggest it's an organized group," Hartley said.
Once thieves obtain credit card information, they can access accounts from other ATMs to withdraw cash, he said.
After hearing reports from other agencies, Los Altos police tracked a spate of fraud reports to the San Antonio Road gas station, where they discovered the skimming device, Hartley said.
Palo Alto police, who did not notify the public about the Wells Fargo incident, heard about it Wednesday, March 19, when the bank notified the department.
An alert Wells Fargo customer, who had recently read about skimming devices, on March 15 noticed that one of the bank's ATMs looked different than the others, Salazar said. He pried off the device and tried to place it through a slot on the bank's door because the bank was closed, Salazar said. When that didn't work, he mailed it to Wells Fargo, which reported the incident to the police March 19, four days after the man discovered the skimmer.
Hartley said he is working with credit card holders who have been affected. Salazar said she expects the bank will use its databases to determine how many customers have been compromised.
She said the bank and police hope to determine how long the skimmer was attached to the California Avenue ATM.
But Wells Fargo customers shouldn't be especially concerned, Salazar said.
"I don't think they should be worried about that ATM in particular. You've got to educate yourself that this type of device is out there and be alert," she said.
All bank customers should regularly monitor their accounts and quickly report unauthorized uses, Salazar and Hartley agreed.
ATM users may even be able to spot skimming devices, which are typically thin devices that fit over the top of the credit card slot, Hartley said. Sometimes they also cover the number keys.
Some skimmers can send information wirelessly while others need to be removed before the thieves can access the credit-card codes, Hartley said.
Skimmers that are handheld or attach to a cash register have been more common in Palo Alto than ATM skimmers, Salazar said. Handheld skimmers can be used in restaurants, she said. She said thieves sometimes manufacture new cards using the stolen information.
Skimming cases are challenging for law-enforcement agencies because often they only receive reports of unauthorized credit-card use. Often, data from a large number of customers reporting fraud is needed to pinpoint a particular device or thief, Salazar said.
Hartley said recent ATM skimming cases have been reported in San Bruno, San Francisco and Mountain View.
"It's not that common and it's not that common in Palo Alto," Salazar said.
"Customer funds are safe at Wells Fargo," spokeswoman Michele Ashley said in an e-mailed statement Monday. "Wells Fargo is thoroughly investigating this matter. We cannot discuss the situation as doing so could jeopardize the investigation."