A new bulletin from Visa indicates that it is increasingly concerned about point of sale terminals being adapted to steal card data over Bluetooth connections.

To combat this threat, Visa advises merchants to scan for Bluetooth signals, which could be evidence of a wireless skimming device transmitting stolen card numbers, according to a Sept. 7 report from StorefrontBacktalk.

A bulletin Visa issued Sept. 1 lists specific units from VeriFone, Hypercom and Ingenico that the card network says are "susceptible to compromise" by this technique. Visa described instances of fraudsters removing the terminals to install skimming hardware, including Bluetooth transmitters, before putting the modified terminals back into use at checkout lanes.

Visa's suggestion to scan for Bluetooth signals goes beyond what is required by the Payment Card Industry Data Security Standard, which instructs merchants to scan for rogue Wi-Fi signals, the article said.