Over eight million Brits have handed over their Chip and PIN details to someone else in the last year, with a quarter of these falling victim to fraud, according to a survey for insurance firm LV=.
An online poll of 3002 people shows 20% have given out their card and PIN number - 85% of these in the past year - to someone else to make a purchase on their behalf or get money from a cash machine.
Around a third of respondents says they have been asked to pay for goods or take money out with someone else's card.
The most popular "PIN pals" are spouses or partners, although children (20%), parents (17%) and friends (15%) are also commonly relied upon to make purchases on other people's behalf.
By far the worst offenders are younger people with over one in three of the under 35s admitting they have asked someone else to use one of their cards. The most common location for 'borrowed' cards to be used is at a cash machine.
For those people handing over details, nine per cent have told someone over the phone, seven per cent have written them down, six per cent have given them face to face in a public place and a few have even sent the details to someone in an e-mail or text message.
LV= also warns that businesses need to pay closer attention as 98% of people who have used someone else's card said they were not caught, leaving retailers open to being targeted by fraudsters.
John O'Roarke, managing director of LV= home insurance, says: "We would strongly urge all card-users not to tell anyone their pin number. Not only does it undermine the security of your account and increases the risk of ID fraud but also card holders could end up out of pocket if they are found to have shared their card details."