How do sitesl like facebook, twitter, reddit, etc etc protect their script?
 

Anyone who works there can just download their script onto a USB drive any runaway with it.. right?

And do what with it? By a clone domain and get a billion people to sign up?

Their IP is the execution, not the script.

those are not one click install scripts, those custom made from scratch , anyways if even i get copy of fb, it will be fucking difficult to run it.
1) they watch their employees emails
2) they have policies/terms for theives , if something caught sharing the code with outsiders.
3) they watch employee's online activity, even plugging usb triggers it.
4) the main core code isnt shared with all stupid/new interns , only major / old coders have acces to ot.
all other coding is done in small parts from each team , so not many have access to whole code.,
5) and many more things, i can think of these for now.,
hope this helps.,

compartmentalisation

They pay their developers enough money.