Uniquely identify one computer

Question

I work for a university, and i\'m implementing a PHP web app that needs to have different behavior when it is visited from one certain computer. The problem i am running in

Answer 1

Im sure you got a very good answer but if you are looking for solution that uniquely identifies the COMPUTER rather than the BROWSER then look in to FLASH COOKIES a.k.a FLASH SHARED OBJECTS.

Theses are more powerful and can be used to store data up to 100KB and remains the same across all browsers that has flash, so it is better solution to uniquely identifying a user