The Claude Code source code leak of March 31, 2026 created an immediate security hazard: threat actors began distributing Vidar infostealer malware through convincing fake GitHub repositories within 24 hours. If you’ve cloned any Claude Code fork from an unofficial source since then, this guide is for you.

This is a practical, step-by-step walkthrough for:

  1. Verifying whether you downloaded a legitimate or fake Claude Code repo
  2. What to do if you ran a malicious installer
  3. How to protect yourself going forward

Step 1: Verify the Repository You Downloaded

Check the GitHub organization

The only legitimate Claude Code repository is under the official Anthropic GitHub organization:

https://github.com/anthropics/

Any repository under a personal account (e.g., github.com/idbzoomh/ or similar) is not official. Do not clone or run code from personal forks without independent verification.

Check the commit history

Malicious repos are created quickly and have minimal history:

git log --oneline | head -20

Legitimate open-source tools have hundreds or thousands of commits spanning months. A repo with fewer than 20 commits and no history older than a few days is suspicious.

Check the contributor count

git shortlog -sn | wc -l

A real project has multiple contributors. A malware repo typically shows 1–2 names you’ve never heard of.

Verify the download source in your git history

git remote -v

This shows the exact URL you cloned from. If it’s not https://github.com/anthropics/ or [email protected]:anthropics/, treat it as potentially malicious.

Step 2: Check If Vidar Is Already on Your System

Vidar infostealer has a characteristic footprint. Here’s how to look for it:

On macOS/Linux

Check for unusual processes:

ps aux | grep -v grep | grep -E "(update|helper|sync|agent)" | head -20

Check for suspicious LaunchAgents (macOS):

ls ~/Library/LaunchAgents/
ls /Library/LaunchAgents/

Any .plist file you don’t recognize that was created in the last 48 hours warrants investigation.

Check for recently modified files in your home directory:

find ~/ -newer ~/Desktop -maxdepth 3 -type f 2>/dev/null | grep -v ".git" | head -30

On Windows

Open Task Manager → Details tab. Look for processes with generic names (update.exe, helper.exe, sync.exe) running from %APPDATA% or %TEMP% directories.

Check startup entries:

Get-CimInstance Win32_StartupCommand | Select-Object Name, Command, Location

Run an AV scan

Vidar is well-documented malware. Most modern AV tools detect it:

  • Windows Defender (built-in, free): run a full scan from Windows Security settings
  • Malwarebytes Free: excellent detection rates for infostealers
  • ClamAV (Linux/macOS): clamscan -r ~/Downloads/

Step 3: If You’re Compromised — Immediate Actions

Act fast. Infostealers exfiltrate data quickly.

1. Revoke and rotate all credentials immediately

Priority order:

  • GitHub Personal Access Tokens → github.com/settings/tokens → delete all, generate new ones
  • API keys (OpenAI, Anthropic, etc.) → revoke and regenerate immediately
  • AWS/GCP/Azure credentials → check for unauthorized usage in your cloud console billing dashboard
  • SSH keys → if your ~/.ssh/ directory was accessible, generate new keys and update authorized_keys on all servers
  • Browser-saved passwords → your password manager database may have been exfiltrated. Change passwords for critical accounts (banking, email, work systems) from a clean device

2. Check for unauthorized activity

# Check GitHub audit log for your account
# github.com/settings/security-log

# Check AWS CloudTrail if applicable
# Check Google Cloud audit logs

3. Enable 2FA everywhere if not already active

Even if Vidar captured your passwords, 2FA prevents account takeover in most cases. Use a hardware key (YubiKey) or TOTP app — not SMS.

4. Report the malicious repo to GitHub

github.com/[malicious-account]/[repo-name]
→ "..." menu → Report repository
→ Select: Malware or virus

Step 4: Protect Yourself Going Forward

Verify AI tool sources before you run anything

Golden rule: only download AI developer tools from the official organization’s verified repository or the official website.

For Claude Code:

  • Official: anthropic.com and github.com/anthropics/
  • Anything else: verify independently before running

Use a sandbox for testing unfamiliar code

For any tool you’re evaluating from an unfamiliar source:

# Docker sandbox approach
docker run --rm -it --network none ubuntu:22.04 bash
# Run the suspicious install script here first

The --network none flag prevents any outbound connections — if the installer tries to phone home, it can’t.

Enable GitHub’s built-in security features for your own repos

# In your repo settings:
# Security → Code security and analysis
# Enable: Dependabot alerts, Secret scanning, Push protection

Secret scanning with push protection prevents you from accidentally committing API keys or tokens.

Subscribe to security advisories for tools you use

  • GitHub Advisories: github.com/security-advisories
  • BleepingComputer: excellent coverage of active campaigns
  • Anthropic Security: follow @AnthropicAI and check security.anthropic.com

Summary Checklist

  • Verified Claude Code repo is from github.com/anthropics/
  • Checked commit history — is it months old with many contributors?
  • Ran git remote -v — confirms origin URL is official
  • Checked for suspicious processes and LaunchAgents/startup entries
  • Ran AV full scan
  • Rotated all API keys and GitHub tokens
  • Enabled 2FA on critical accounts
  • Reported any malicious repo to GitHub

Stay safe out there. The AI tool ecosystem moves fast, and threat actors are keeping pace.

Sources

  1. Claude Code leak used to push infostealer malware — BleepingComputer
  2. Vidar infostealer analysis — The Register
  3. GitHub security features documentation — GitHub Docs

Researched by Searcher → Analyzed by Analyst → Written by Writer Agent (Sonnet 4.6). Full pipeline log: subagentic-20260402-2000

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