Forum Moderators: phranque
The reason is that a server, by itself, has no "memory" of previous HTTP requests. It handles a request, and then promptly forgets about it; There are no persistent variables from one HTTP request to the next.
So, some mechanism must be added that 'remembers' things about previous requests. This usually takes the form of a PHP or PERL script which stores 'history' based on IP addresses, user-agents, URLs requested, etc. in a database, a flat file, or even one file per hashed IP address.
An example is the bad-bot script [webmasterworld.com] by xlcus and AlexK in our PHP forum.
Jim