The skimmers are capable of printing a receipt even if they're offline
Fraudsters often harvest credit card details by tampering Point of Sale (POS) devices from various merchants. While in some cases they alter the existing devices, they can also simply replace them with cleverly-designed "fakes."Brian Krebs has identified one cybercriminal that sells two types of pre-hacked Verifone POS devices on the black market: Verifone vx670, which costs $2,900 (€2,200), and Verifone vx510, which comes at a price of $2,500 (€1,900).
The skimmers are designed to store card data and PINs on their internal memory. They’re mostly recommended for fraudsters who work (or who have accomplices) at restaurants or retailers.
The most interesting thing about these particular skimmers is that they work even if the machine is offline. They’re programmed to display that the transaction has been successfully completed and they even print out a receipt, despite the fact that they’re not connected to the payment system.
They can also be programmed to display a connection error.
The seller of these POS skimmers has recorded a video (available above) to demonstrate how the devices work.