Looks like grc.com got twit-dotted & digg-dotted. Go to twit.tv and read about the security news concerning the wmf exploit. Steve Gibson's site attracted too much attention and looks like the site is has gotten slammed.
Try ping www.grc.com and you can see that the traffic is quite heavy.
Listen to Podcast 22 at www.twit.tv (This week in Tech) by Leo Laporte about the controversy on the origins of the WMF vulnerability.
I linked here from DIGG since digg won't allow a direct link to a page that is down (grc.com). There's no other discussion about this anywhere else on the net that I know of.
It may be that everyone is downloading the WMF Vulnerability tester from GRC.com? Anyone have any mirror sites?
You could try the coral cache at http://www.grc.com.nyud.net:8090 but even the coral cache can't seem to help grc right now.
ADDENDUM: As of 22:40 PST the site is backup. Download the KnockKnock.exe tool from www.grc.com to see if your computer is patched against the WMF vulnerability
ADDENDUM: It was DDOS'd which makes more sense
From Steve Gibson on www.twit.tv: "it was about a six-hour DDoS attack lasting from about 3:00 PM PST to 9:00 PM PST."