Customization specifications are XML files that contain guest operating system settings for virtual machines. You create customization specifications with the Guest Customization wizard, and manage specifications using the Customization Specification Manager.

vCenter Server saves the customized configuration parameters in the vCenter Server database. If the customization settings are saved, the administrator, and domain administrator, passwords are stored in encrypted format in the database. Because the certificate used to encrypt the passwords is unique to each vCenter Server system, reinstalling vCenter Server, or attaching a new instance of the server the database, invalidates the encrypted passwords. The passwords must be re-entered before they can be used.