A data breach at Revolut, in which hackers claim to have stolen the details of nearly 700 “crypto whale” accounts and are now demanding a $2m ransom, has reignited concerns about the traceability of digital assets and the risks of holding them.

On Wednesday, a note on the website of the hacker group iamnotavillain ordered the bank to pay “6,000 XMR” – shorthand for a notoriously hard-to-trace cryptocurrency called Monero – “otherwise all the data will be sold, and the blood will be on your hands”. Revolut said it had received no direct contact from the group, and it is not clear whether a ransom has been paid.

Despite the colourful threat, the attack on Revolut, which happened days before the bank announced that it would…