A client called about its website being down. Even a simple page requested would show a blank screen, but without any browser error. The website was ping-able with decent responses. The IP returned from the DNS was correct - I had to check the IP because the client just renewed the domain registration and I was afraid the renewal somehow caused the IP associated with the website to be changed. That was not the case. Just to be sure. I also got the confirmation by "View Source" in the browser which showed the correct site info.
I then reviewed the System event log and noticed an recent installation of Windows Security updates KB941644 and KB943485. I tried to call Microsoft Product Support Services at 1-866-PCSAFETY for free security updates support to find out if Microsoft had any knowledge, but got no answer. I searched the web and found some complaints related to the updates, and one particular about the proxy being messed up and the user having to uninstall the updates to fix the problem. My client did not use a proxy server but that message told me that the updates might have changed something on the web server to interfere with Internet browsing or even page rendering. I checked the web server's log and noticed 404 errors associated with the GET from external Ips - and interestingly, from Intranet Ips, browsing the web site had not problem. Another important piece of info was that from the web server, I could not browse www.msn.com, www.microsoft.com, etc - the display showed the same blank screen just as an Internet user would get trying to browse my client's website, even though I could browse other web sites such as www.google.com. With the above facts, I first uninstalled the updates, but that did not fix the problem. So, something else was changed. I then went to Internet Options and restored the default settings. Whala! Everything started to work again.
That was a very unfortunate experience. My client's production web site was down for quite some time just because Microsoft sent out the updates without any warning about the potential effects. In this case, my client did nothing wrong, and it just followed Microsoft's recommendation. I hope Microsoft will be more thorough in QA and provide better guidance about its future updates.