Unique environment variable?

Hi,
I'm seeking a pretty unique environment variable.(Like a hardware address)
It should be used to make sure that a user is only logging on from a specific computer.
I have login and password additionally saved into a cookie so it is ok if the variable isn't really/very unique. I would just like to use it as an additional security feature.

I can't use the IP address because some users might have a permanent internet connection. Anyone has an idea? Is it possible to get an irq list or the graphic cards ID from the client?
Thanks for any help,
Jimmy

Intel tried implementing something like this with the Pentium III chip, and raised a mighty stink from privacy advocates. It's unlikely you'll see anything like this. Think about it -- it would make it possible to track where people go on the Internet.

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Alan Little
Holotech Web Design
www.holotech.net/

" it is ok if the variable isn't really/very unique"
Sorry if you didn't understood me right. I would just like to add such a thing as an additional security feature. I don't expect that everyone uses the the same graphic card. So getting an ID of it would do it. I do not build my security system on this so it doesn't really hurt if people are using the same graphic cards. I don't want to fix on graphic cards. Its just an example.

Jimmy.