About 70% of all Bitcoin Unlimited nodes went out of service after as information about a fault and possible exploit in the BU code spread over the internet.

According to Node Counter, on 14 March the total number of reachable BU nodes hit 776, but then suddenly dropped to about 245. As of 15 March, the alternative bitcoin client accounts for 530 available nodes.

The share of BU nodes in the bitcoin system has shrunk from over 12% to 8.36%.

The bag found in the BU code could cause a ban of a node after receiving a specific message.

“Sending an invalid GET_XTHIN is a serious misbehavior and any node doing so will be DOS100 banned immediately. Also sending a GET_XTHIN with an invalid message type will also cause the sender to be banned,” the official BU page on GitHub stated.

The bug was also spotted by the Bitcoin Core developer Peter Todd, who suggested in a tweet that the error in the BU code could have been around for as long as a year.


Soon after the information was circulated, the BU devs released an update with a fix.

At the same time, BU supporters turned on Peter Todd, who, according to them, had spread the information about the bug but did not say a word about the solution. Some noted that Todd published his tweet an hour after the problem was fixed.


In January, the bitcoin entrepreneur and prominent Bitcoin Unlimited supporter Roger Ver lost $12,000 due to an invalid BU block. The rejection of the block by Bitcoin Core nodes resulted in the pool losing about 13 BTC in premium. The invalid block was mined by bitcoin.com, owned by Roger Ver.

Elena Platonova