Add-ins are supplemental programs that extend the capabilities of Microsoft Expression Web by adding custom commands and specialized features.
When you disable an add-in, its features and commands are removed from Expression Web, but the add-in itself remains on your computer for easy reloading.
You can enable and disable add-ins while Expression Web is running but you must close Expression Web before you can install or uninstall add-ins from your computer.
For more information about enabling and disabling individual add-ins, see Manage Add-ins dialog box
Security vulnerabilities in external files or controls may extend to Web pages that use those items. For example, external script files (files with a .js extension), custom ASP.NET controls, or other items, may pose a security risk. Be sure your add-ins, themes, executables, scripts, controls, or other files come from trusted sources.