Tesco has confirmed that is has deactivated around 2,000 tesco.com accounts after details were shared online.
"We take the security of our customers’ data extremely seriously and are urgently investigating these claims," a company spokeswoman told Pocket-lint.
The details allowed anyone who saw the list to access login details and passwords, and therefore personal details and Tesco Clubcard voucher information.
"We have contacted all customers who may have been affected and are committed to ensuring that none of them miss out as a result of this," added Tesco.
Users who have been affected should have had their accounts deactivated, but it's probably a good suggestion that Tesco.com customers change their password now to be on the safe side.
"We will issue replacement vouchers to the very small number who are affected."
The number of accounts compromised pales in comparison however to the number of online shoppers the company has on a weekly basis.
In the six weeks running up to Christmas last year, Tesco says it processed over three million online grocery delivery orders.