Three people were arrested recently in southern Maine, facing charges relating to a scheme to “clone” credit cards at gas pumps.

Police say the three had installed a machine called a skimmer, which steals card data that can then be transferred to a blank card and used for illegal purchases.

Those phony charges will show up on the true owner’s monthly statement, so it’s up to all smart consumers to check those statements closely. Disputing them will take time, and so will the process of getting a new card.

A better idea is avoiding any card machine that appears to have been altered.

Look around the card slot. If you see scrapes, scratches or torn labels that raise your suspicions, make your purchase the old-fashioned way: Pay with cash. You might see that one pump seems to stick out farther than the rest. That can be a sign that it’s been tampered with.

Thieves can install a skimmer in a matter of seconds. Even with attendants on duty, they can’t watch every pump every second. The crooks often use double-stick tape to put their skimmers in place. If the card slot looks odd, give it a wiggle. It might just drop right off the pump.

The Minnesota Department of Commerce has classified skimming at gas pumps as an “emerging threat.” In Eagan Minnesota, police and most local gas station operators have teamed up in an effort to defeat the skimmers.

Stations that take part in the SkimStop program place stickers on their pumps, warning potential thieves that the pumps are checked daily. The stickers bear serial numbers, so they can’t be easily duplicated. If the seal on the security label is tampered with, the pump can be checked to make sure a skimmer hasn’t been installed.

Eagan police say thieves in one case captured the data of 157 victims. They used the data they stole to buy gift cards and made some $21,000 in illegal purchases.

“For the cost of some stickers, we can solve a lot of problems,” Officer Aaron Machtemes told me.

The SkimStop program began in March. “We haven’t had a skimming device in our city since,” Machtemes said.

At least one Maine chain of convenience stores tried another version of sticker, but company officials declined a request for an interview. Some stickers do not carry a serial number and are readily available for purchase online. Thieves can buy a roll of 500 stickers for about $70, do their dirty work and slap a new sticker on a pump, leaving consumers — and likely most store employees — none the wiser.

William Lund is superintendent of Maine’s Bureau of Consumer Credit Protection. Lund said the arrest of the three suspects in the Brunswick case shows that some thieves consider Maine as ripe for ripping off as anywhere.

“It all boils down to people in Maine realizing that we don’t get a free pass when this technology becomes common,” Lund said. He urged consumers to be observant and cautious when using credit or debit cards in any public setting. More on this topic next week.

Consumer Forum is a collaboration of the Bangor Daily News and Northeast CONTACT, Maine’s all-volunteer, nonprofit consumer organization. For assistance with consumer-related issues, including consumer fraud and identity theft, or for information, write Consumer Forum, P.O. Box 486, Brewer, ME 04412, visit http://necontact.wordpress.com or email contacexdir@live.com.