Hackers claiming responsibility for a data breach at Revolut have threatened to sell confidential records of hundreds of customers unless the British online bank pays a $3mn ransom within 24 hours. The group, calling itself iamnotavillain, published the ultimatum online on Wednesday with a digital countdown clock.

The message told Revolut to pay "6,000 XMR / $3,000,000 . . . otherwise all the data will be sold, and the blood will be on your hands". XMR is the cryptocurrency Monero. The group told the FT it was using the website to make demands for the first time and that there had been no negotiations with Revolut.

The breach is understood to have affected at least 680 customer accounts. Hackers obtained files by compromising an Italian government email system, posing as law enforcement to demand information on specific Revolut client accounts. The group said it selected targets using blockchain analysis to identify accounts with significant crypto holdings.

Since launching in 2015, Revolut has become Europe's biggest fintech, operating in over 30 countries with 80mn customers. It was recently valued at $115bn. Revolut declined to comment on the ransom demand.