Nearly 70% of nodes running Bitcoin Unlimited went offline today as word emerged of a bug in the software’s code.

The bug opened a vulnerability through which a certain kind of message sent to nodes could cause them to be taken offline. Nodes are responsible for validating the transactions on a blockchain, maintaining a copy of the transaction history’s entire record and essentially enforcing the rules of the network through the code.

The issue was originally flagged on GitHub by BU developer Peter Tschipper. Details then spread on social media, sparking widespread commentary from both supporters and critics of the project.

That discussion – and highlighting of the bug – was followed by an apparent exploit that sent the node count plunging. BU developers have since moved to release a patch for the bug.

During the attack, the BU node count slipped to as low as 252, according to cryptocurrency data site Coin.Dance, while data site Bitnodes showed roughly 265 nodes online at the time.

In total, as many as 780 BU nodes were online prior to the drop, data from Coin.Dance shows, and as of press time, 240 BU nodes are online. To get a sense of the scale, roughly 6,100 nodes make up the bitcoin network’s global ecosystem, according to Bitnodes.

BU is an alternative implementation of the bitcoin software, which among other changes seeks to put in place a user-configured transaction block size as a means to scale the network. The software project emerged amidst the wider debate over ways to scale the transaction capacity of the network.

BU has drawn both strong supporters and sharp critics, with some arguing that it provides a path to scale the network while others have criticized its approach to expanding the block size.

Read CoinDesk’s recent explainer on Bitcoin Unlimited here.

Chart via Coin.Dance; Image via Shutterstock