Police are warning shoppers to use different passwords for their online Black Friday shopping after a man was arrested for alleged cyber offences against Tesco.
The 28-year-old was arrested in Middlesbrough after the supermarket giant found someone trying to breach its online system and reported it to police.
No customer details, financial or personal were obtained.
The Metropolitan Police's cyber crime unit Falcon said it is investigating a technique known as "diagonal brute forcing" in which username and passwords obtained from previous hacks are used to check if that same combination of username and password has a valid account with other retailers.
If a match is found, the account can be accessed.
Detective Inspector Garry Lilburn, of Falcon, said: "Having one password for all your online accounts is like having a key which unlocks your house, car and office. If you lose that key, you place yourself at greater risk.
"With Christmas approaching and individuals having more online shopping accounts than ever, we would urge everyone to make sure they have different passwords for each retailer they visit, to prevent their accounts being breached in this way."
A Tesco spokesman said: "Our security systems identified some irregular activity and we acted swiftly, alerting the relevant authorities including FALCON. No financial or personal customer information was obtained.
"We continue to advise customers to use different passwords across their accounts to be as secure as possible online."
