Criminals can work out the card number, expiry date and security code for a Visa debit or credit card in as little as six seconds using guesswork, researchers have found.
Experts from Newcastle University said it was “frighteningly easy” to do with a laptop and an internet connection.
Fraudsters use a so-called Distributed Guessing Attack to get around security features put in place to stop online fraud, and this may have been the method used in the recent Tesco Bank hack.
According to a study published in the academic journal IEEE Security & Privacy, that meant fraudsters could use computers to systematically fire different variations of security data at hundreds of websites simultaneously.
Within seconds, by a process of elimination, the criminals could verify the correct card number, expiry date and the three-digit security number on the back of the card.