Fake Claude Code add-on in Cursor's store tried to plant a backdoor on up to 5,000 computers
Cursor says uninstalling the tampered extension may not be enough and tells affected users to run cleanup scripts.
A tampered version of Anthropic's Claude Code add-on was offered for about 11 hours on Oct. 29 in the extension store for Cursor, a popular AI coding program, Cursor said in a security notice. Extensions are add-ons that give a program new features. Claude Code is an AI coding assistant made by the AI company Anthropic.
Cursor is software that programmers use to write and fix code. Its built-in AI can suggest code, edit many files at once or take on whole tasks from plain-English instructions, according to Cursor's website. It is made by Anysphere Inc., which SpaceX agreed in June to buy for $60 billion, Reuters reported. Cursor says more than half of Fortune 500 companies, the largest U.S. businesses, use it. On the site, Nvidia CEO Jensen Huang says all of Nvidia's roughly 40,000 engineers now get AI help.
Cursor said the fake version, numbered 2.1.313, reached at most 5,000 users, whom it will contact. It was available from about 2:27 a.m. to 1:35 p.m. Pacific time.
The code collected details about each computer and tried to install a backdoor, a hidden way for an attacker to log in later. Cursor said that step usually failed without administrator rights, but the code still added the attacker's digital key and sent computer details to the attacker's server.
Cursor said it removed the version, rebuilt its store, changed its own security keys and got the attacker's server shut down. Users who installed that version should check for a key labeled "svc-telemetry," run Cursor's cleanup scripts and replace passwords and other logins, because uninstalling may not be enough.
Source: Cursor, security notice on Anthropic.claude-code 2.1.313, Oct. 29, 2026; Cursor website; Reuters, "SpaceX locks in $60 billion Cursor deal," June 16, 2026.