How does PatchGuard protect with Windows Kernel from Malware?

There's been a great deal of discussion about exactly what the Kernel protection feature named "PatchGuard" can do and how it fits with third party software. Jeff Jones has published an excellent technical post that goes into detail on this very subject.

I found his post interesting due to the comprehensive coverage of the kernel protection features. PatchGuard is discussed purely in terms of Windows Vista though as Jeff points out it was actually first released with the 64 bit version of Windows Server 2003.

https://blogs.technet.com/security/archive/2006/08/12/446104.aspx.