The company’s operators, who are based in the Netherlands, were found not to have followed the guidelines for managing user information.
Kraken says it’s working with the Financial Conduct Authority to investigate the breach, and that it will restore services in due course.
It says that all users of the exchange are being provided with a refund of any funds lost, and it is working with law enforcement agencies in the UK to determine whether criminal charges will be brought.
In a statement, Kraken said: ‘We are extremely sorry for the inconvenience this may have caused and for any concerns that may have been raised.
‘We have taken steps to ensure that the exchange remains open and operational in the interests of our users and the wider crypto community.
‘This is not an isolated incident and we will continue to work with the FCA to identify any further issues that may arise in the future.
‘In the meantime, we will be fully refunding any funds in the event that the site is closed down for any reason.
‘We are in discussions with law enforcers and will provide them with any further information they require.
We sincerely apologise for any inconvenience this might have caused to our users.
‘Kraki will continue working with our users to provide a safer and more reliable marketplace and we are committed to the future of crypto and the Bitcoin community as a whole.’
Kraka’s CEO, John Cappas, confirmed that the firm had shut down the exchange.
He told reporters that the incident had occurred on December 2, and was caused by a bug in the software that Kraken uses to manage user accounts.
Kraker is a Bitcoin exchange.
It is based in Amsterdam, and allows users to buy and sell virtual currency.
It was not immediately clear if the UK government had issued a ban on cryptocurrency exchanges, or if it had asked the European Commission to regulate them.