"So I saw this awesome issue where IE 7 hangs indefinitely and stops responding on the third request for a page. Yes the 3rd request.

Basically IE7 is limited to 2 active connections per server inside one browser window (including all tabs) and these connections were being wasted in unresponsive requests for favicon.ico.

 

Here's what I learned. 

At the time I did not know that IE browsers attempt to retrieve favicon.ico from ther root of your website every time they make a page request. (How to add a favicon to your website)

Also, I did not know that this generated a 404 error in the IIS log every single time they tried to retrieve it unsuccessfully.

Also, I did not know that some web application firewalls (firewalls that constantly learn and update themselves to prevent security breaches) will actually stop responding to requests that are consistently turning up 404 as a safety measure.

Columnist Ivan Ristic comments on web security "The point is that you are not looking for a single suspicious action any more - you are using counters to look for anomalies. Other examples include looking for IP addresses with too many failed requests (too many 404 responses typically point to web application scanner activity), enforcing session inactivity timeouts, session duration timeouts, and so on."

Lastly, and the final piece of the puzzle. I did not know that:

Internet Explorer 7 (IE7) has an extremely long time out for requesting favicon.ico. ("a hex with a lot of F's" said the Microsoft Support Engineer)"