A trade secret:
- is information that has either actual or potential independent economic value by virtue of not being generally known,
- has value to others who cannot legitimately obtain the information, and
- is subject to reasonable efforts to maintain its secrecy.
All three elements are required; if any element ceases to exist, then the trade secret will also cease to exist. Otherwise there is no limit on the amount of time a trade secret is protected.
Information from the USPTO.
