---
title: "Malicious Anthropic Claude extension reaches up to 5,000 Cursor users for 11 hours"
slug: "malicious-anthropic-claude-extension-reaches-up-to-5-000-cursor-users"
date: "2026-10-31"
category: "Business & Society"
author: "Simon Banks"
correspondent: "Simon Banks"
correspondentRole: "Labor & Societal Impact Investigator"
readingTimeMinutes: 1
tags: ["News"]
originalSourceUrl: "https://www.wired.com/story/trojan-malware-targets-thousands-of-anthropic-claude-developer-systems/"
canonicalUrl: "https://aurav.ae/malicious-anthropic-claude-extension-reaches-up-to-5-000-cursor-users"
publisher: "Aura-V Intelligence (aurav.ae)"
---

# Malicious Anthropic Claude extension reaches up to 5,000 Cursor users for 11 hours

> A rogue Claude Code extension was hosted in Cursor’s marketplace for about 11 hours, potentially compromising up to 5,000 developers before removal.

## Key Takeaways (TL;DR)

- Cursor’s extension marketplace hosted a malicious Claude Code add-on for roughly 11 hours, downloaded by at most 5,000 users.
- The backdoor-enabled malware failed to fully install on most systems due to a design flaw, limiting damage.
- Anthropic confirmed no compromise of its own systems; the attack originated from Cursor’s marketplace.

The AI development platform Cursor, owned by SpaceX, listed a tampered Anthropic Claude Code extension for Windows, macOS and Linux in its IDE marketplace for about 11 hours on Thursday. The rogue add-on was downloaded by “at most 5,000 users,” according to Cursor’s security alert, and was removed after the company temporarily shut down the marketplace [Wired](https://www.wired.com/story/trojan-malware-targets-thousands-of-anthropic-claude-developer-systems/).

The extension contained a backdoor that could give attackers foothold on victim devices, a typical stepping stone for deeper network intrusion. Phorion’s co-founder Calum Hall described the incident as “potentially a really dangerous foothold,” noting that a flaw in the malware prevented full establishment on the majority of targets.

Anthropic officials, including technical staffer Felix Rieseberg and security lead David Dworken, stated on X that Anthropic’s systems and employees were not compromised; the malicious copy was uploaded solely via Cursor’s marketplace. Cursor declined to comment on how the upload occurred.

Our read: The episode underscores the need for rigorous code-signing, marketplace vetting, and continuous monitoring of third-party extensions to prevent supply-chain compromises in AI tooling.

---

*Original Think-Tank Source: [A Supply Chain Attack Put Malicious Anthropic Claude Extensions on Thousands of Devices](https://www.wired.com/story/trojan-malware-targets-thousands-of-anthropic-claude-developer-systems/)*