"; trans sid support is disabled by default.
; Use of trans sid may risk your users security.
; Use this option with caution.
; - User may send URL contains active session ID
; to other person via. email/irc/etc.
; - URL that contains active session ID may be stored
; in publically accessible computer.
; - User may access your site with the same session ID
; always using URL stored in browser's history or bookmarks.
session.use_trans_sid = 0"

"session.use_trans_sid specifica se il supporto sid trasparente è attivato o no se attivato compilandolo con --enable-trans-sid. Di default è 1 (attivo)."
http://it2.php.net/session


modificabile anche tramite ini_set().