Trade secret protection is provided under individual state laws. It protects the owner against use or willful disclosure of a secret process or application by others, but not independent discovery (as patents do). Information protected by trade secret maintains its status as long as the information is not publicly disclosed. This has been used extensively in the minicomputer and mainframe world because these programs and code are licensed to individual customers, not the mass market. Some microcomputer software is released with "shrink wrap" licenses intended to maintain trade-secret status, protecting the object code portion of the package. Trade secret has no limitation on its duration, but doesn't protect against independent creation, reverse engineering or accidental disclosure.
See also Patents, Copyrights
