Microsoft has always been blamed for being a monopoly. But Dan Geer went further ahead to term it the cause of a monoculture. Here's the famous paper where he comapred the Internet to Microsoft Monoculture! According to him the network could be sharing a single flaw and can be brought down by a virus exploiting that flaw! Pretty interesting concept... though a bit far fetched I'd say.

Most of the latest viruses have spread more due to gullible users and poorly maintained systems. The OS is just a part of the whole ecosystem that could turn into a monoculture. A careless system administrator who poorly manages his network or a naive user who believes that its perfectly fine to open attachments from unknown people make the network more vulnerable than just the machines.

Thinking about viruses and patches, I wonder why doesn't Microsoft or any other software vendor deploy a viruslike patch management system. I system which tries to find vulnerable computers by attacking and just patches whenever it comes across one. This would be so easy to manage and deploy for an organization. Particularly where not all of the machines are connected to the internet and hence cannot benefit from the automatic patches provided by Microsoft.