A slightly more useful post ... I've found that the firewall built into my Netgear router spots GRC scanning my PC and goes into an "anti Denial of Service (DoS)" mode, whereby it ignores
all incoming traffic from GRC for a period.
During this time, GRC report all ports as Stealth - even ports that I
know are intentionally open - because the anti-DoS behaviour is in force.
So I always try a few services to make sure that I'm getting credible results - eg try
http://probe.hackerwatch.org/probe/probe.asp and
http://www.speedguide.net/scan.php for a 2nd and 3rd opinion.
RC