Checking with GRC Gibson research, sometimes I find Port 554 open: probing again only this port I find it Stealth.
What does it mean ? Is there a specific program using this Port ?
Thank You in advance

Versione ZoneAlarm Extreme Security:11.0.000.020
versione vsmon:11.0.000.020
Versione driver:11.0.000.009
Versione motore antivirus:8.3.0.13
Versione file DAT delle firme antivirus:1100707136
Versione antispam:6.3.1.4973
ZoneAlarm Browser Security: 1.5.393.18
Rilevatore spyware di ZoneAlarm ForceField:1.2.104.0
WIN 7Pro/64 -Firefox 16 & IE9