If you were looking for a good reason to protect your ATM card, the latest news from the California Attorney General's Office provides it.

Authorities have filed charges against three men they say stole $150,000 from consumers' bank accounts, using "skimmers" placed inside gas pumps in Northern California. The episode could give pause to anyone using a debit card at a "pay at the pump" station.

A "skimmer" is an electronic device that intercepts a consumer's debit card information when they swipe it. Sometimes its placed over the real card slot. Sometimes its embedded in the pump itself. If it captures the users credit card number and PIN, the operator can later clean out the unsuspecting consumer's bank account.

"These thieves broke into gas station pumps and installed devices that collected customers' debit and credit card numbers and ATM PINs," Attorney General Jerry Brown said. "Later they used that stolen information to create fraudulent cards, make purchases and withdraw thousands of dollars from victims' accounts." 

The three men face 42 counts of felony theft and one count of conspiracy. If convicted on all charges, the three could each face up to 31 years in prison. 

"Skimming" scams have been around a long time. In March, the California Attorney General's Office took over prosecution of the case from the Contra Costa District Attorney's office because the crimes occurred in multiple jurisdictions throughout Northern California.

In their high-tech crime spree, the three traveled to gas stations and banks across the Bay Area in a rented Cadillac Escalade. From November 2009 to February 2010, they are believed to have stolen $158,800 from 196 people. 

How a "skimming" scam works

To be able to install a device to steal debit card information usually requires access. In this case, Brown says the defendants acquired keys to unlock various kinds of gas station pumps.

Once they opened the pumps, they were able to connect two cables inside to their two-inch electronic device, which looked like a circuit board encased in electrical tape, and recorded ATM and credit card data as well as victims' PINs.

No tampering was visible on the outside of the pumps. The trio would later return to retrieve the skimmers, which took less than 20 seconds. 

The investigation began in February when police in Solano and Contra Costa counties reported an increase in identity theft and a 7-11 Store employee in Martinez noticed a skimming device inside a gas pump. Police removed the device, replaced it with a mock device and conducted 24-hour surveillance. Two of the men were arrested when they arrived to remove the device, Brown says. In total, seven devices were found inside gas pumps in Martinez, Benicia, Livermore, Hayward, Oakland, San Mateo and Sacramento. 

While allowing thieves access to your bank account usually means the money can't be recovered, Brown says in each of these cases, banks have reimbursed the victims.