Tesco is set to reissue a deluge of loyalty cards as it believes the personal information of up to 620,000 of its loyalty customers has been hacked from another organisation.

The grocer said that a collection of stolen data from another organisation has been utilised to try to access up to 620,000 of its Clubcard accounts.

The retailer emailed impacted shoppers to let them know and has cancelled all affected vouchers.

Tesco has stressed that no financial information has been breached as a result of the attempted hack and that its decision to reissue the Clubcards has been taken as a precautionary measure.

The grocer has also asked affected customers to reset their passwords and has apologised for any inconvenience caused.

A statement from the grocer said: “We are aware of some fraudulent activity around the redemption of a small proportion of our customers’ Clubcard vouchers.

“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.

“At no point was any customer’s financial data accessed.

“We believe that someone has stolen password/username combinations from other website(s) and used them to try to access Tesco sites – where customers used the same username and password.”

The attempted data breach comes as another bidder for Tesco’s Thai and Malaysian business subsidiary enters the fray.

Thai billionaire Charoen Sirivadhanabhakdi’s holding company TCC Global is understood to have obtained a $10bn (£7.8bn) two-year loan to finance a deal for the grocery division, with a combination of local and international banks lined up to fund the bid.

It is thought that this bid will make Sirivadhanabhakdi the third Thai conglomerate to make a formal bid for Tesco’s business subsidiary in the region.

The Wall Street Journal, which first reported the prospective bid, said Tesco’s Thai operations could be valued at about $7bn (£5.5bn), while the Malaysian division could fetch more than $1.5bn (£1.2bn).

Sirivadhanabhakdi has amassed a retail empire including the Big C hypermarket chain. The group acquired French grocer Casino’s Thai hypermarkets in 2016 for $3.5bn (£2.7bn).

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