Fake Claude Code add-on was posted on Cursor's extension store

Anthropic says someone slipped a fake version of its Claude Code add-on into Cursor's extension marketplace. The company says it did not build or publish that copy. It calls the version "tampered," meaning it was altered by someone else.

What happened

Cursor is a code editor, the program developers use to write software. Like many editors, it has a marketplace where people share add-ons that extend what it can do. Claude Code is Anthropic's coding assistant, and it has an extension for this kind of editor. According to Anthropic, a bad actor used access to Cursor's marketplace to publish a altered copy under that name.

Why it matters

Add-ons often get wide access to the files on a computer. A fake one could expose your files and passwords. That is why it matters where an add-on comes from, not just what it is called.

Who can relax

Anthropic says this was not a compromise of its own systems or employees. It says it is working with Cursor on the incident. People who do not use Cursor, or never installed a Claude Code extension there, are not described as affected.

What is not known yet

The material does not say how many people installed the fake copy, how long it was available, or what it did. It also does not explain how the bad actor got marketplace access. Those answers may come from Anthropic and Cursor.

What to do

The alert box above lists the steps. In short, check which Claude Code extension you have and who published it, and watch for guidance from both companies.