On BitcoinTalk forum, the company explained how hackers stole the Bitcoins; Placing multiple withdrawls requests at the same time will result in negative balance but still the request is being processed.
"Another design flaw is that withdrawals should be queued at every step of the way. This could not have happened if withdrawals requests were processed sequentially instead of simultaneously" the forum post explaining another bug reads.
One of the forum's member gave a link to the attacker's bitcoin address "https://blockchain.info/address/1Ktq7TE3J5vZ3c99M5weqKfFcNkHQdqPrq". It appears the loss is around $50,000(76BTC).
The owner of Poloniex said he will take the full responsibility and will repay the debt of BTC. However, due to shortage of 12.3% in funds, the company will temporarily deduct 12.3% balance from all accounts.
"If I had the money to cover the entire debt right now, I would cover it in a heartbeat. I simply don't, and I can't just pull it out of thin air." he said.