A greater number of ATM skimming incidents now involve so-called “insert skimmers,” wafer-thin fraud devices made to fit snugly and invisibly inside a cash machine’s card acceptance slot. New evidence suggests that at least some of these insert skimmers — which record card data and store it on a tiny embedded flash drive  — are equipped with technology allowing them to transmit stolen card data wirelessly via infrared, the same communications technology that powers a TV remote control.

Last month the Oklahoma City metropolitan area experienced rash of ATM attacks involving insert skimmers. The local KFOR news channel on June 28, 2017 ran a story stating that at least four banks in the area were hit with insert skimmers.

The story quoted a local police detective saying “the skimmer contains an antenna which transmits your card information to a tiny camera hidden somewhere outside the ATM.”

Financial industry sources tell KrebsOnSecurity that preliminary analysis of the insert skimmers used in the attacks suggests they were configured to transmit stolen card data wirelessly to the hidden camera using infrared, a short-range communications technology most commonly found in television remote controls.

Here’s a look at one of the insert skimmers that Oklahoma authorities recently seized from a compromised ATM:

In such an attack, the hidden camera has a dual function: To record time-stamped videos of ATM users entering their PINs; and to receive card data recorded and transmitted by the insert skimmer. In this scenario, the fraudster could leave the insert skimmer embedded in the ATM’s card acceptance slot, and merely swap out the hidden camera whenever its internal battery is expected to be depleted.

Of course, the insert skimmer also operates on an embedded battery, but according to my sources the skimmer in question was designed to turn on only when someone uses the cash machine, thereby preserving the battery.

Thieves involved in skimming attacks have hidden spy cameras in some pretty ingenious places, such as a brochure rack to the side of the cash machine or a safety mirror affixed above the cash machine (some ATMs legitimately place these mirrors so that customers will be alerted if someone is standing behind them at the machine).

More often than not, however, hidden cameras are placed behind tiny pinholes cut into false fascias that thieves install directly above or beside the PIN pad. Unfortunately, I don’t have a picture of a hidden camera used in the recent Oklahoma City insert skimming attacks.

Here’s a closer look at the insert skimmer found in Oklahoma:

A source at a financial institution in Oklahoma shared the following images of the individuals who are suspected of installing these insert skimming devices.

As this skimming attack illustrates, most skimmers rely on a hidden camera to record the victim’s PIN, so it’s a good idea to cover the pin pad with your hand, purse or wallet while you enter it.

Yes, there are skimming devices that rely on non-video methods to obtain the PIN (such as PIN pad overlays), but these devices are comparatively rare and quite a bit more expensive for fraudsters to build and/or buy.

So cover the PIN pad. It also protects you against some ne’er-do-well behind you at the ATM “shoulder surfing” you to learn your PIN (which would likely be followed by a whack on the head).

It’s an elegant and simple solution to a growing problem. But you’d be amazed at how many people fail to take this basic, hassle-free precaution.

If you’re as fascinated as I am with all these skimming devices, check out my series All About Skimmers.