The security of millions of bank accounts is being put at risk because people write down their PIN numbers.
Consumer group Which? found that many people keep a note of their PIN in their wallet or handbag. Equially concerning, it found some people tell their code to someone else.
Research by Which? estimates that four million debit card holders and three million credit card holders are at risk of having their accounts raided because they haven’t kept their PIN a secret.
Of those who wrote their number down, 9% kept a note of it at work.
Banks and credit card firms can refuse to pay compensation if they can prove a cardholder has been negligent with their PIN or other security details, so keeping it to yourself is twice as important.
"The results show that too many consumers are putting their finances in jeopardy by not taking simple precautions," says Martyn Saville, senior researcher at Which?.
"Writing down your PIN is like leaving your door open when you leave the house."
Meanwhile, a specialist police unit, the Dedicated Cheques and Plastic Crime Unit (DCPCU), revealed it recovered 7,900 counterfeit cards in 2009. It also recovered 29,300 compromised or stolen card numbers last year.
The bank-sponsored police unit says its work to target organised fraud gangs led to estimated savings of £24.5 million in 2009.
This significant sum helped to contribute to the reduction in annual card fraud losses announced by the banking industry last month. Total card fraud losses in 2009 decreased by £160 million from the previous year, amounting to £440.3 million.
Detective chief inspector John Osibote, who leads the DCPCU, says: "With fraud loss savings estimated at £3.5 million per month, the unit has been instrumental in helping drive down card fraud. We want to send out a loud and clear message to the organised criminal gangs who are behind the lion's share of fraud on UK cards that we can, and will, track them down."
How to keep your bank account safe from fraudsters:
* Use different PINs for different cards. If possible memorise the PINs and don’t write them down. If you do keep a note of the number, keep it separate from the card.
* Don’t tell anyone else your PIN. Neither your bank nor the police will ever ask you for it.
* Try not to let your card out of your sight when making a transaction and don’t leave it behind the bar in the pub to run a tab.
* Check receipts against statements carefully. Contact your card company immediately if you find an unfamiliar transaction.
* Store your statements, receipts and financial documents safely and destroy, preferably shred, them when you dispose of them.
* Cut expired cards through the magnetic strip and chip when replacement cards arrive. Sign new cards straight away.
* When entering your PIN, use your free hand and your body to shield the number from prying eyes or hidden cameras.