[thelist] HTTP_REFERER v user agent

[alex beston]

Hi All

in http://uk.php.net/reserved.variables

it mentions this:

"The address of the page (if any) which referred the user agent to the 
current page. This is set by the user agent. Not all user agents will 
set this, and some provide the ability to modify HTTP_REFERER as a 
feature. In short, it cannot really be trusted "

This is a bit worrying. Does anyone know which user agents (eg browsers) 
prevent this?

I need this because I'm working on visitor tracker system and I need to 
ensure that all visitors orgins are known: ie which ads they have come 
in on.

Maybe the only way to do this, rather than putting code into the entry 
page, is to rely on the access logs?

Thoughts?

Alex