It's impossible to keep a secret among thousands of people. Whoever sends a memo to everyone@bigcorp must assume that it reaches dozens of journalists' buddies, moles of the competition, perhaps even spies of foreign nations and definitely hundreds of folks who will bellow about it in bars in the evening.
https://plus.google.com/+VicGundotra/posts/MFrDF3W4RJL
https://plus.google.com/+LarryPage/posts/A2gm48nzitx