The cyber-attack knocked out servers dealing with cleared derivatives, sparking trade reporting and matching problems for brokers and rival processing services around the world.

The Russian ransomware gang claiming responsibility for the attack - LockBit - has now told Reuters that it has received the ransom in exchange for a decryption key to unlock infected machines. The money, they say, came from a "philanthropist".

The group had threatened to publish stolen ION material if it did not get the ransom by Saturday.

The ordeal is far from over for ION, according to Lou Steinberg from cybersecurity outfit CTM Insights, who has told Bloomberg that it could take months to get the firm’s system’s running properly.