Trusted operating systems were originally designed to enforce military security policies on government computers. However, with the growth of Internet-based commerce, the need for TOS-based security is no longer restricted to government environments.
"The threats posed by the modern computing environment cannot be addressed without secure operating systems. Any security effort which ignores this fact can only result in a 'fortress built upon sand.'" (Loscocco, 1998)
Certain threats, such as buffer-overflow/stack-overwrite attacks, administrator hijacking, multi-network communication, improper application interaction, and other application software bugs, can only be controlled via the operating system, which can impose limits on all software.
A trusted operating system does not take the place of encryption, intrusion detection, or authentication, but often makes a firewall unnecessary. It strengthens all other security mechanisms. Trusted OS's can create partitions for applications and resources, so damage from compromised programs is limited.
Only trusted operating systems can provide the stability and security required for critical commercial servers.