As we expected Microsoft is releasing an out-of-band patch tomorrow 12/17 for a critical Internet Explorer 7 vulnerability. The browser flaw had been disclosed roughly one week ago as a zero day vulnerability and active exploits have been around the internet for that timeframe as well. The work-arounds provided by Microsoft were very technical and quite cumbersome to implement making it imperative for Microsoft to release a fix as quickly as possible.
Given the typical requirements for developing, testing and packaging the changes to a program as widely deployed as Internet Explorer we have seen one of the fastest turnarounds possible. Moving faster would require having specific mechanisms in the base code of the application allowing to push out changes in a less disruptive way and would require an extensive rewrite of Internet Explorer. Other browser providers have an edge here as they already have update mechanisms included in their products.