The present invention is directed to a system and method of securely providing extensible third-party plug-ins to user computers. The system enables third-parties to authenticate themselves to user computers before a user computer is allowed to load the plug-ins. The system also creates separate processes that are spawned from a main process in order to securely execute the third-party plug-ins. Security is further enhanced by assigning a privilege level to the separate process that is lower than the main process.