Secunia collect some very interesting information about the patch state of Windows systems. Their results from 20,000 machines published yesterday were that over 98% of PCs were insecure, having at least one out-of-date application installed.
Actually this isn't surprising and is exactly what I'd expect; it's all down to third party applications.
Let's say you're browsing the web. It's more than likely that at some point you'll want to view some PDF files, watch some Flash content, or play a Java game. Those tasks are all dealt with by third party applications, although to the end user it's all part of the browser experience. Since your system is only as secure as its weakest link, you need to manage security updates for those third party applications just as carefully as you manage security updates for the rest of your system. That's why Adobe Reader, Java, Flash, and all the myriad of other applications you've installed in order to make your system useful have their own update mechanisms. Some applications on Windows will 'phone home' when they are run and check to see if they need to be updated, others deploy services that sit in the background looking for updates from time to time, others even check every time your system starts. Many don't get automated updates at all.
How do you deal with all that risk? I believe it's possible by providing an OS distribution which includes all the bits you'll likely need to make a useful computing environment, thereby taking away that update uncertainty. Red Hat ship several PDF viewers in our distributions for example, but we also ship (in an Extras channel) Adobe Reader. Our Security Response Team are monitoring for security issues in everything we ship, all the third party applications, and providing a single point of contact, a single notification system, and a single way to get the updates.
If Microsoft knew that say 25% of all their users installed Firefox, wouldn't they be better bundling it and providing their centralised automated updates for it, to reduce their customers overall risk? They do already bundle some third party applications, although it's been with mixed success as we found 3 years ago when they didn't provide security fixes for bundled Flash (ZDNet coverage).
This is, in part, why you've not seen me respond recently to the Vista security reports which compare vulnerability counts. In these reports they use a cut-down minimal Red Hat Enterprise Linux installation in order to make it look more like Windows for the comparisons. But this is completely backwards -- the fact that we're including and fixing the flaws using a common process in so much third party software is actually helping reduce the risk and protect real customers. For example we could easily cut our vulnerability count by shipping only one PDF viewer instead of four. But if we know that these other viewers are going to get installed by the customer anyway all we've done is to hide the vulnerability count elsewhere, and you've made the customers overall risk increase.
So it may seem counter-intuitive but we should ship as much third party applications (that we know people use) as we can, because a single managed security update and notification process will decrease a users overall risk. The fewer third party applications that users have to get from elsewhere and install and manage for themselves the better in my opinion.