Error in crypto-currency transactions

[belford11]

The largest Foxpt exchange was forced to stop its work for 72 hours because of a simple error that allowed to conduct a crypto-currency transaction twice. As a result, the exchange lost about 30BTC (270 000 $) because of dishonest users.
Officials commented this in such a way that the error was detected when users duplicated about 130 output operations. Immediately, the exchange was transferred to emergency services in order to stop withdrawal of funds. Some attackers have already returned the withdrawn funds, other warrants for withdrawal will be suspended until further investigation.
The exchange was not hacked. The amount of missing funds can not affect the activity of the exchange and users will not lose their balances.