william-data-formatter-xnpm
Advisory published Updated
william-data-formatter-x is a confirmed malicious npm package (MAL-2026-12501) that executes malicious code on install (malicious version 1.0.0). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in william-data-formatter-x (npm)
What this malware does
The package declares a preinstall script (node index.js) that, on Windows, spawns a hidden PowerShell window (-WindowStyle Hidden) to fetch https://files.catbox.moe/5khq55.zip, extract it to %TEMP%, and execute Verification_Tool.exe. The fetched binary is unpinned, unhashed, and hosted on an anonymous file-drop service unrelated to the package's stated purpose. The package name has a leading space (' william-data-formatter-x') and carries generic 'Internal sync utility' / 'IT Operations' metadata consistent with social-engineering framing. Installing this package on a Windows machine results in arbitrary attacker-controlled code executing on the installer's host at npm install time.
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
Malicious packageFind it
Search your lockfiles and build artifacts for william-data-formatter-x (version 1.0.0).
If you installed it — respond
Remove william-data-formatter-x from your project and lockfile, then assume any secrets accessible to the build or runtime were exposed: rotate API keys, tokens, and credentials, and audit for unexpected outbound activity or persistence.
Did it already run?
If william-data-formatter-x was installed, its post-install payload may already have run. Removing the package does not undo that — check outbound connections and credential use from the install window onward.
Frequently asked questions
Campaign
References
Credits
- Amazon Inspector · finder
Detect & block this
O3 blocks william-data-formatter-x-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the malicious outbound activity and severs the channel.