The company initially estimated that up to 5,000 users could have been affected, highlighting the security risks associated with compromised software development tools. The compromised extension packages, identified as Anthropic.claude-code versions 2.1.312 and 2.1.313, were distributed through Cursor’s VS Code extension marketplace during an about 11-hour window on October 29, 2026, from 2:27 a.m. to 1:35 p.m.
Cursor said the malicious software was not created by Anthropic and that it found no evidence that other versions of Claude Code were compromised. The attack targeted developers’ workstations, which often have access to software repositories, cloud platforms and credentials used to build and deploy applications.
