I am using session_start() and session_id() trying to  identify visitors
to my site. 
Problem: the session.cookie_lifetime is set to 0, but with IE5 the
session does not expire when closing all browser windows, clearing cashe
and or deleting cookies.
The session expires as expected when using NS4.

The only thing I can figure out is that IE5 isnt actually closing, but
keeping the session even though I close the browser windows, but that
sounds insane!

But... how can I solve this?

THE SESSION SETTINGS:
session.auto_start Off Off 
session.cache_expire 180 180 
session.cache_limiter nocache nocache 
session.cookie_domain no value no value 
session.cookie_lifetime 0 0 
session.cookie_path / / 
session.cookie_secure Off Off 
session.entropy_file no value no value 
session.entropy_length 0 0 
session.gc_maxlifetime 1440 1440 
session.gc_probability 1 1 
session.name PHPSESSID PHPSESSID 
session.referer_check no value no value 
session.save_handler files files 
session.save_path /var/php-sessions /var/php-sessions 
session.serialize_handler php php 
session.use_cookies On On 

 

After doing a lot of testing I have found that this problem is caused by
Outlook Express. Outlook Express seems to somehow be running an instance
of Internet Explorer, and while having Outlook open the sessions that
are supposed to be expiring are being kept alive. Im using Win 98. If
anybody else encounters the same problem...

There's little PHP can do for broken clients. Bogus.