Bitcoin Forum

The value of bitcoins plunged in early August after Bitfinex, a major exchange based in Hong Kong, said it had been hacked and funds stolen.
It was a serious security breach that could weaken investors' confidence in bitcoin exchanges and cramp growth in the popularity of the digital currency.
"Today we discovered a security breach that requires us to halt all trading on Bitfinex, as well as halt all digital token deposits to and withdrawals from Bitfinex," the exchange said in an Aug. 2 blog posting. "We are investigating the breach to determine what happened, but we know that some of our users have had their bitcoins stolen."

http://asia.nikkei.com/Markets/Currencies/Hong-Kong-hack-highlights-weak-security-at-bitcoin-exchanges