Here is a free script writing program that's right online. Very easy to use. :)

http://www.scriptbuddy.com/

Since it's web-based, is there a security issue? Could someone else access your script?

You can put a password on your script so no one else can see it. Or if you do want people to see it you can publish it and let others have alook at it. The site publishes the scripts and you can read them right from there. :)

Ahhh, but can you print out your script in proper Hollywood standard format? I looked at it as well and it doesn't break it down in number of pages, which is a very important feature.