The polymarket-stake-kelly-math-check npm package version 3.5.2 contains malicious code that executes a postinstall hook to download and run unverified remote code. This remote payload is fetched from a mutable, unauthenticated URL controlled by the package publisher, allowing arbitrary code execution on the host system. The package's installation process silently swallows errors, potentially hiding malicious activity. Any system with this package installed should be considered fully compromised, and secrets on that system must be rotated immediately.