An operating system and method for use include a core function module, or basic kernel, providing fundamental operating system support and one or more add-on modules that allow customization of the operating system as desired. Add-on modules may provide support or extended capability to the computer including hardware, applications, peripherals, and support. A digital signature may be used to confirm the integrity of an add-on module prior to installation. Certification may be verified to determine if installation of the add-on module is authorized. By withholding certification, a service provider may manage illegal or undesired modifications to a provided computer. Digital rights management may be used to enforce terms of use of the add-on module in keeping with licensing arrangements.