Ciao Maurizio,
prova allora questo:
Options +FollowSymlinks
RewriteEngine On
# If referer is not from your landing site (www.example.net) under which
# the Moodle instance has been deployed (www.example.net/moodle):
RewriteCond %{HTTP_REFERER} !^https?://www.example.net [NC]
# and referer is not blank or "-":
RewriteCond %{HTTP_REFERER} !^-?$
# then redirect the initial request to your landing site, the Joomla! instance:
RewriteRule ^(.*)$ http://www.example.net/ [R,L]
HTH,
Matteo