If anyone tells you something, no one else can learn that information. The limitation on this is that the information cannot already be common knowledge; if more than about three-dozen people already know a piece of information, this power won't work on it. It also only applies to information that both parties believe to be true.
If someone tries to share this information, they'll be unable to. If someone tries to read the information, their eyes will just slide past it. If someone observes something that should clue them in, they'll dismiss it.