Google Tag Manager incorporates several features to help ensure the security of your websites and apps. Administrators can restrict tag deployment for their installations to allow only specific tags to be deployed. You can also configure Google Tag Manager to work with a Content Security Policy implementation. Custom templates provide a framework to develop your own tag and variable templates that work within a secure, controlled, sandboxed environment. Server-side Tag Manager helps to secure your tag configurations and data by moving client-side JavaScript off of the browser.
In addition to the developer-level security features, you may also want to familiarize yourself with Tag Manager's access controls, 2-step verification, and malware detection.