GILROY (CBS SF) — A spike in credit card fraud cases in Gilroy over the weekend appears to have been caused by a well-placed credit card skimming device at a gas station, police said.

The Gilroy Police Department said some $50,000 was stolen from at least 40 victims, the majority who used their credit or ATM cards at a Valero gas station at 1190 First Street in Gilroy.

Investigators found a skimming device inside the housing of one of the gas pumps and it was not visible from the outside of the pump, police said.

It’s believed the skimmer was in use at the gas station for at least a week until its was removed Monday.

“They successfully pulled out a thousand dollars out of my account,” said one victim, Robert Heslop.

A Facebook forum listed at least 100 people who shared similar stories after visiting that Valero gas station.

Some victims, however, said they never went to that gas station. “We feel like it was the Safeway on First St.,” said victim Susan Felios. “We can’ be sure.”

Felios also said her and her family’s credit cards all have security chips in it, which are designed to protect against such fraud. “So chip cards do provide protection from this kind of fraud, but they aren’t a guarantee,” said CNET reporter Laura Hautala. “There are machines that can do skimming [of chip cards].”

Police believe the number of victims will continue to grow from this particular skimming case.

People who may have purchased gas at that station in Gilroy were urged to check their bank or credit card statments and call the Gilroy Police Department if they believed they have been victimized.