If an application uses a third-party assembly that requires a private data store, isolated storage can be used to store the private data. Isolation by user, domain, and assembly ensures that only code in a given assembly can access the data, and only when the assembly is used by the application that was running when the user created the store, and only when the application is run by the user who created the store. Isolation by user, domain, and assembly keeps the third-party assembly from leaking data to other applications. This isolation type should be your default choice if you know you want to use isolated storage but are not sure which type of isolation to use.