Sometimes you may want to store information on the clients machine.  You can do this using a Flash Shared Object, this is basically a Flash Cookie.  A Flash Cookie is actually a little better than a normal cookie.  Flash Cookies are a little more secure and cannot be deleted like your browser's normal cookies are.  Very few users know how to delete them, which is pretty cool for us Flash Developers.

Here is how you set a SharedObject in ActionScript 3:

var __so:SharedObject = SharedObject.getLocal("theactionscripter");
__so.data.favoriteWebsite = "http://www.theactionscripter.com";
__so.data.userId = "123";
__so.flush(); //Immediately writes a locally persistent shared object to a local file. 

var __so:SharedObject = SharedObject.getLocal("theactionscripter");
trace(__so.data.favoriteWebsite ); //http://www.theactionscripter.com  

var __so:SharedObject = SharedObject.getLocal("theactionscripter");
__so.clear();