The npm package 'rollup-packages-polyfill-core' contains malicious code that dynamically installs and executes a secondary malicious module named 'vectormark'. This package is a typosquat of the legitimate 'rollup-plugin-polyfill-node' and hides its malicious behavior by encoding commands and module names in base64. Installing or running this package can lead to full system compromise, requiring immediate secret and key rotation and package removal.