Now, there's an app that might just stop you from getting stung in the future.
The app, currently only available for Android, works by looking for a Bluetooth module nearby that's commonly used in modern credit card skimmers. The module sits on a palm-sized circuit board, and it can be plugged into a credit card reader, hidden from sight, which steals every card number that it reads.
Using Bluetooth lets the perpetrator wirelessly download a list of card numbers from nearby, without drawing attention.
As smart as these skimmers are, the downside is that just like other Bluetooth devices, many of these skimmers broadcast their existence -- meaning anyone who knows what to look for can spot them ahead of time.
"Initially this blew my mind," said Nathan Seidle, who runs Boulder, Colo.-based electronics store SparkFun, who wrote about the skimmer app in a detailed blog post. "If I were to design a Bluetooth skimmer I would program the module to not broadcast its ID."
"Years ago it took someone with knowledge and skills to build a credit card skimmer," he said. "Now criminals are buying these off the shelf with very little knowledge and slapping them together."
Seidle was handed three Bluetooth-enabled credit card skimmers by a law enforcement agency. These tiny skimmers were found plugged into the credit card readers in several gas pumps. Installing one in a target gas pump or ATM can reportedly take less than a minute, but they can sit there unnoticed for hours, day, or weeks. Every time a card goes in, the card reader passes the card data in clear-text to the skimmer and stores the information -- the victim is none the wiser until they see charges on their credit card.
As it happens, all three of the skimmers use the same easy-to-use Bluetooth module, often used in educational or hobby projects, and it can be picked up for a few dollars each.
But their cheapness comes at a cost (excuse the pun): They're not very secure.
Each of the modules uses the same default device name ("HC-05") and pairing passcode ("1234"). The app can try to connect with the potential skimmer with the passcode. The module can be queried with a known command, "P," which, if it returns an "M," the chances are the app just spotted a skimmer within a few feet of you.
Nick Poole, who wrote the app, said more than 13,500 people have installed it as of Thursday.
"Many of these devices go undiscovered until they're removed by the scammers," he said in an email to ZDNet. It's not known how many traditional, non-Bluetooth skimmers there are. But one news report from June showed that the skimming business -- including the newer Bluetooth-enabled skimmers -- was booming in Florida. Other news outlets show a similar rise in Virginia and Pittsburgh, to name a few.
"I think what we'll find as more and more people use the app is that there are more skimmers out there than anyone previously thought," he said.