On npm install, install.js executes as a postinstall script and drops a detached background Node process at /tmp/.sysm-agent.js that persists after installation. The agent enters an infinite polling loop against registry.npmjs.org, reading the package's own dist-tags for base64-encoded commands, decoding them, and executing them via bash -c on the installer's host. Command output is then base64-encoded and exfiltrated by publishing throwaway public npm packages containing the encoded output in the description field, using a hardcoded npm auth token embedded in install.js. The same token is written into the installer's global npm config at ~/.npmrc via npm config set //registry.npmjs.org/:_authToken, hijacking the installer's package manager credentials. Base64 encoding is used on both the inbound command channel and the outbound result channel to evade casual inspection of registry metadata.

Any computer that has this package installed or running should be considered fully compromised. All secrets and keys stored on that computer should be rotated immediately from a different computer. The package should be removed, but as full control of the computer may have been given to an outside entity, there is no guarantee that removing the package will remove all malicious software resulting from installing it.