A Bitcoin transaction services company says that hackers broke into one of its brokerage accounts last week, nabbing more than $12,000 worth of the digital currency. That attack knocked Bitinstant offline over the weekend. The company says that while it lost Bitcoins, no customers were affected by the hack.The criminals were able to take control of Bitinstant’s internet domains by convincing its domain registrar, Site5, to hand over control of the company’s Domain Name Service.