Sessions Issue

Hey Guys,

I am having one hell of a problem that I cannot figure out for the life of me. I have set up a super simple CMS for a client. Each different page of the CMS has and include file called session.php.

session.php


session_start(); 
$username = $_SESSION['siteadmin'];
if (!$_SESSION['siteadmin']){
	header( 'Location: login.php?status=2' );
}

Every now and again, random things would disappear from the database. So, I setup a crude log system that logged any action through the CMS. Well, it happened again. The logs show this:


Logged in  	                        **.**.237.209  	17:18  <-- thats me
Deleted board member id 12 	195.42.102.25 	16:49 
Deleted board member id 15 	195.42.102.25 	16:49 
Deleted board member id 8 	195.42.102.25 	16:49 
Deleted board member id 10 	195.42.102.25 	16:49 
Deleted board member id 9 	195.42.102.25 	16:49 
Deleted board member id 4 	195.42.102.25 	16:49 
Deleted board member id 3 	195.42.102.25 	16:49 
Deleted board member id 5 	195.42.102.25 	16:49 
Deleted board member id 6 	195.42.102.25 	16:49 
Deleted board member id 11 	195.42.102.25 	16:49 
Deleted board member id 7 	195.42.102.25 	16:49 
Deleted review id 2 	        195.42.102.25 	16:49 
Deleted review id 3 	        195.42.102.25 	16:49 

and that goes on for a couple pages. It doesnt even show 195.42.102.25 logging in! Last time it happened with 195.128.18.19. How are they computers loading the window without a session variable? Is there a security hole in my code that I am completely overlooking?!

Any insight on this issue would be awesome.

Thanks,