More than 600,000 Tesco Clubcard accounts have been blocked after scammers tried to steal points from customer accounts.
The supermarket believes a database of stolen usernames and passwords from other platforms had been used on its site to gain access.
620,000 accounts blocked
A total of 620,000 Clubcard accounts have been blocked in an effort to protect customer points. Only a small number of customers are believed to have had their points stolen, but Tesco said these would be returned and new vouchers issued.
The supermarket said that no financial data has been accessed, and its IT systems had not been hacked.
In an email issued to potentially affected customers, Tesco wrote, “We recently became aware of some fraudulent activity on your Clubcard account, which included an attempt to access your Clubcard vouchers.
"We picked this up quickly and, to be on the safe side, blocked your account immediately. This means that, when you next try to sign in, you'll be asked to reset your password.
"As an extra precaution, we will reissue you with a new Clubcard number.”
Advice for customers
Tesco has issued all affected customers with a new Clubcard and has advised them to reset their passwords. Customers can continue to use their existing cards while they wait for their new one to arrive, and they will not lose any points.
A spokesperson for the supermarket told The Sun, “We have strict security measures in place and our priority is protecting our customers.
"Our internal systems picked this up quickly and we immediately took steps to protect our customers and restrict access to their accounts.
"We have asked customers affected to reset their passwords and are contacting customers whose Clubcard vouchers may have been affected to let them know that we will replace these vouchers and issue new Clubcards, as a precaution."
How does the loyalty scheme work?
The Clubcard loyalty scheme gives customers one point for every pound they spend in Tesco scores, and one point for every £2 that is spent on fuel.
A total of 100 points amounts to £1, and the supermarket sends out vouchers for every 150 points you have collected every three months.
These vouchers, which last for two years, can then be used to spend as face value in Tesco stores, or can be converted into three times their value using the supermarket’s rewards platform.