Ben Fritz wrote about the insane lengths that movie studios often go to, to prevent their scripts from leaking:

• Christopher Nolan and J.J. Abrams are (in)famous for the secrecy they demand for their scripts. For Star Trek Into Darkness for example, those who wanted to read the script had to find the one physical copy tucked away in a nondescript location and printed on red paper which is difficult to photocopy…and read.
• The script for Pacific Rim could only be read on a special tablet app that would self-destruct after a few hours.
• Even movie adaptions of books – which anybody can read the plot of – command heightened secrecy. Every copy of The Hunger Games scripts have a few words changed. By checking out which version of the script leaks they know exactly who to fire.
• Studios are doing this because often times when a script is leaked critics pan the writing, depressing theater attendance from audiences who never even give the film a chance.

Read more about some of the other measures used to protect scripts, movies that have famously leaked, and more over here.

Source: The Wall Street Journal