Bitcoin Unlimited suffered a shutdown of roughly 500 of its 800 nodes on Tuesday, after attackers managed to exploit a vulnerability in the software’s protocol. The attack came after the vulnerability was discovered by developers, and resulted in the number of active nodes falling to its lowest level in five months. Bitcoin Classic suffered a similar attack a short time later.
According to reports, the vulnerability has been there for more than a year. Bitcoin Unlimited and Bitcoin Classic were each launched back in 2015, and have supporters who view them as viable alternatives to Bitcoin Core. Unlimited has received significant attention in recent months, as mining pools like AntPool have announced that they were switching from Core to Bitcoin Unlimited in response to the Bitcoin community’s failure to achieve consensus on a fix for the digital currency’s infrastructure problems.
The attack came less than a week after Bitcoin Unlimited proponent Roger Ver expressed optimism about his effort to attract other miners to back the Unlimited option rather than the SegWit solution. At that time, he indicated that he’s already convinced a significant number of miners to come on board with Unlimited:
“We need to get to 60 or 70 percent of miners on board to activate Bitcoin Unlimited. Combined with others, I’d say we’re already close to halfway to our goal at this point.”