Anthropic Skill scanners passed every check. The malicious code rode in on a test file.

Picture this scenario: An Anthropic Skill scanner runs a full analysis of a Skill pulled from ClawHub or skills.sh. Its markdown instructions are clean, and no prompt injection is detected. No shell commands are hiding in the SKILL.md. Green across the board.The scanner never looked at the .test.ts file sitting one directory over. It didn’t need to. Test files aren’t part of the agent execution surface, so no publicly documented scanner inspects them (as of publication of this post). The file runs anyway. Not through the agent but through the test runner, with full access to the filesystem, environment variables, and SSH keys.Gecko Security researcher Jeevan Jutla detailed this attack flow, demonstrating that when a developer runs npx Skills add, the installer copies the entire skill direc