Records show that funds in a variety of crypto-currencies were withdrawn from the DForce platform based in China.
A sum of $10m was taken in Ethereum, for example, while a further $10m was taken in digital coins tied to the US dollar and $4m in other coins.
Roughly the same amount has now been returned - although in a different mix of crypto-currencies.
DForce is an online service that allows users to make crypto-currency transactions with one another.