A poisoned package is a dependency, installer, or update that has been altered to include malicious code or behavior while still appearing legitimate. It may be published under a real package name, slipped into a dependency chain, or recommended by a compromised tool.
This matters because modern development relies on package managers and automated installation flows. If a developer, assistant, or build system trusts the package, the attacker can gain execution inside the workstation, CI pipeline, or repository. A poisoned package may steal secrets, open a backdoor, tamper with builds, or fetch additional malware. In supply-chain attacks, the package itself becomes the delivery mechanism, so defenders must verify sources, pin versions, review dependency changes, and scan for unexpected scripts or network activity during install.