Hide text from a thread

[HumanNature]

Hello, I want to know if someone can tell me about a hack to hide text when you write a thread.

The idea is that the user knows that there is a text but he only is able to read it if he push over the "hide text".

Grrr I don´t know how to explain me better.... something like when you can´t read a php code in this forums if you are not logged and showing as licenced

Thanks