Sainsbury's shoppers are being warned of a flaw in the Nectar points system after an innocent customer lost 14,000 points to criminals.
Caroline Enderby discovered last month that her points had been fraudulently used at a Sainsbury's petrol station in July without her knowledge.
Despite Sainsbury's, which owns Nectar, claiming the issue affects only a small proportion of its 18 million members, the frequency of reported thefts suggests the problem may be more widespread.
When Enderby contacted Nectar to alert them to the fraud, she was advised that the points would be refunded if she visited the station the fraud occurred, which provided some relief.
Sainsbury's shoppers will be able to use offers more GETTY/PAHowever, when she got there, the store manager was confused and unable to issue a refund this large.
She said: "This I did, although the store manager was bemused as to why I'd been been asked to do this as he cannot instigate a return of that number of points.
"On reporting back to Nectar, I was informed that my points would be refunded and a new card issued."
Yet, when her new card arrived, the points had not been refunded.
Nectar then advised her to report the theft to the police, citing her occasional use of the fuel station as a reason for not refunding the points.
A flaw in Nectar's system that means criminals seemingly can use customer's points without having the physical card.
Unlike bank cards, Nectar cards lack chip technology and secondary authentication, making them potentially easier targets for criminals.
These types of fraud cases have been occurring since the loyalty scheme's launch in 2002.
Shoppers earn one Nectar point for every £1 spent in Sainsbury's stores and online, or for each litre of fuel purchased.
Points can also be accrued at other participating retailers. However, the ease with which fraudsters can apparently use customers' points without possessing the physical card is concerning.
Following the confusion, Sainsbury's eventually issued an apology to Caroline and refunded her points.
A spokesperson stated: "We have contacted Ms Enderby to apologise for her experience and arranged for her Nectar points to be refunded to her new account. We have also added 2,000 extra points to her account for the inconvenience."
A Nectar representative later clarified that the advice to visit the petrol station was incorrect.
They told Enderby: "I'm sorry to hear that this has happened and can assure you this is not the correct process.
"This has now been fed back to the colleague you received this advice from to ensure this does not happen in future."