The use of audio technology to record data stored on the magnetic stripe on the backs of all credit and debit cards has been well understood for many years. The basic method for conducting these attacks was mentioned in a 1992 edition of the hacker e-zine Phrack (the edition that explains audio-based skimmers is Phrack 37). Since then, other electronics enthusiasts have blogged about their experiments with sound skimmers; for example, this guy discusses how he made a card reader device out of an old cassette recorder.
Recently, I had a chance to chat via instant message with a hacker in Eastern Europe who sells both audio-based ATM skimmers and the technology needed to decode audio skims or “dumps.
When we walk around NYC we’re always looking for one of these “ATM Skimmers” to see how and what they’re using, so far we haven’t seen a single one.