Securing Use of PHP site

Hello all, I have recently built a site using PHP. I was a little loose with GET and POST methods because I was using it for personal/private use. Now I am thinking of going public and allow different companies to use the site. I want to secure and hide as much data as possible to guard against user abuse. I have several instances where I use the GET method to pass IDS. I can use a POST but even that is visible in the source. How does one allow for processing but never really let the user see that actual ID? Do I use a HASH for IDs? Do I need to get more familiar with SESSION VARS. I am doing some experimenting. Any words of wisdom or resources would be helpful. Thanks! Don Wieland D W D a t a C o n c e p t s ~~~~~~~~~~~~~~~~~~~~~~~~~ donw@dwdataconcepts.com Direct Line - (949) 336-4828 Integrated data solutions to fit your business needs. Need assistance in dialing in your FileMaker solution? Check out our Developer Support Plan at: http://www.dwdataconcepts.com/DevSup.html Appointment 1.0v9 - Powerful Appointment Scheduling for FileMaker Pro 9 or higher http://www.appointment10.com For a quick overview - http://www.appointment10.com/Appt10_Promo/Overview.html