Kitchenware retailer Lakeland has suffered a "sophisticated and sustained" cyber-attack, where hackers gained access to its two encrypted databases.
The company's managing director, Sam Rayner, said that there is no evidence that any data has been stolen, but all customer passwords used on the website have been deleted.
When customers' next log-in to their Lakeland account they will be asked to reset their password and provide a new one. It is also advised that if customers' were using the same password on other accounts, these should also be changed as soon as possible.
Rayner said: "We deeply regret that this has occurred and apologise for the inconvenience caused. The security of our customers' data is hugely important to us and we are devastated to have fallen victim to these criminals.
"This has occurred despite the best efforts of ourselves and the industry leading IT company that runs our website for us to use the best security systems available. We are committed to protecting our customers' data and will continue to seek additional measures to ensure the integrity of our systems."
Lakeland was unable to confirm which IT company hosts its website, but it said that the cyber criminals used a "very recently identified flaw" in the Java software used by the servers running the site.
Dodi Glenn, director of security content management at ThreatTrack Security, said that Lakeland should now be working to establish whether any sensitive data was taken by the hackers.
"It is common practice to purge passwords in the event someone suspects a compromise of their database," said Glenn.
"While customers may be alarmed as is natural in these circumstances, Lakeland should work with the authorities to identify what information was leaked.
"Customers should have the right to know if their credit card numbers were stolen. Lakeland and others should take note that being proactive instead of reactive is the best approach, because brand reputation is priceless."