The Bitcoin exchange Bitstamp has announced it is suspending withdrawals as a result of the same transaction malleability bug that triggered a freeze at the M. Gox exchange earlier this week. According to Bitcoin core developer Jeff Garzik, the issue is more widespread than the team initially realized, and other software may need to be patched. "It's mainly a nuisance," Garzik told The Verge, "forcing everybody to stop and fix their website software and Bitcoin wallets." BitStamp says none of the funds in its system have been lost, but some transactions from the past two days have been preemptively halted while the company implements a fix.
At the same time, there's reason to believe other exchanges may be at risk. Speaking to Coindesk, Blockchain developer Andreas Antonopoulos said he expects other exchanges to follow Bitstamp's lead, suspending withdrawals as they rework their systems to fend off the ongoing attacks. The transaction malleability bug (explained in detail here) exists across the Bitcoin system, but since exchanges have addressed it in different ways, the level of actual vulnerability varies greatly from site to site. Now that the bug is public knowledge, attackers are eager to find the most vulnerable targets, testing out exchanges in brute force attack. In a later tweet, Antonopoulos described the Bitstamp attacker as "someone who read about Gox and decided to shake any remaining bugs loose."