In Apple's case, this is well-documented in several public articles and books, such as the Jobs biographies and any of the "expose" articles that come out the week of a new iPhone release.
> Apple closely monitors all communication on its corporate network and routinely plants false information with employees in an effort to track leaks.
[0] http://www.zdnet.com/article/apples-secret-society/
> Apple closely monitors all communication on its corporate network and routinely plants false information with employees in an effort to track leaks.
[0] http://www.zdnet.com/article/apples-secret-society/