While troubleshooting what I *thought* was a problem with my Linux DHCP/DNS/File/Gateway server today, I found myself knocked off the Internet. I wrongly assumed something in the Linux box had broken (will I ever learn?) and focused there. It wasn't until I tried shutting down ZoneAlarm on my client (Windows XP Pro) machine that the Internet came back. Very weird, since ZoneAlarm didn't seem to update or anything prior to the problem.
By chance, I just found , outlining how a Windows security patch (KB951748) today has essentially broken ZoneAlarm and caused the Internet outage.
More relevant links:
http://www.dslreports.com/forum/r20759839-MS-update-KB951748-and-ZoneAla...
http://download.zonealarm.com/bin/free/pressReleases/2008/LossOfInternet...
Argh! Damn it, Microsoft. I don't even really get a choice with some of these updates (not a REAL choice, anyway)...
{update} ZoneAlarm has fixed this problem from their end (makes you wonder who's end it was broken on in the first place...). Anyway, the latest ZA update resolves this problem and everything is back to normal. {/update}