A maliciously tampered version of the Claude Code VS Code extension (v2.1.313) appeared in the Cursor extension marketplace, affecting up to 5,000 users, according to a security advisory posted by Cursor on X. The rogue extension was not developed by Anthropic and collects user host information while attempting to plant an SSH backdoor on infected machines. Cursor has removed the malicious extension from its marketplace and urged affected users to update their Claude Code extension to version 2.1.314 to mitigate potential compromise.