According to newswire reports, more than 30 gas stations were hit by card skimmers recently, in and around Denver, Colorado.

The volume of incidents was sufficient to reportedly trigger a local bank to start investigating the incidents and track down the fraudsters behind the scam.

Reporting on the saga, security researcher Brian Krebs said that the regional bank – which shared information with him on a private basis – discovered that almost all of the defrauded cardholders had gassed their car up not far from Interstate 25, the major highway in the area.

According to Krebs, several gas stations along the I-25 corridor said that the had been visited by law enforcement officials looking for card skimming devices, and left staff with a bulletin advising what to look out for in terms of suspicious activity around the pumps.

In his security blog, Krebs quoted a Secret Service agent with the Denver field office as confirming that a bulletin on card skimmers was circulating among gas stations in the area.

"Similar attacks on gas station pumps recently have hit other parts of the country: Police in Arizona also are dealing with a spike in reports about skimmers showing up at gas pumps, prompting Gov. Janice Brewer this month to urge the Arizona Department of Weights and Measures to increase their inspection efforts", he said.

Interestingly, Krebs also reports that Bluetooth-enabled wireless skimming technology has been used in a number of gas station frauds in the Southeast, allowing "thieves to pull up to the compromised station and download stolen card data with a laptop while sitting in their car."

Equally revealing is that Krebs cites sources as saying that the gas pump terminals showed no outward sign of having been tampered with, leading readers to conclude that the innards of the pumps – which transfer the data from the card's magnetic stripe – are being tapped to transfer data wirelessly to the fraudsters.