Let me tell you how I delayed WinXP SP2 for a month. My software (BlackICE) was on the list of software that had to work. When they made major changes to the kernel network stack, my software broke. They grabbed their reverse engineers to figure out why. What they discovered was that my software doing something evil, patching the kernel's network stack when our software was loaded. That's tricky on a multi-CPU system with warring instruction/data caches. We wrote a patent on how to do it reliably without crashing the system. We searched through the kernel to find the location we needed to patch, looking for a certain pattern of bytes. They changed the network stack so that thing we were patching no longer existed. So to make our software work, the inserted that pattern back into the kernel. As packets arrived, the new function would jump to that pattern, and then after, jump right back. This way, we could find the pattern and patch it -- and thereby patch the intended function. Some Microsoft lawyers wanted to sue us for violating the software license agreement, which forbids reverse engineering, which we had to do in order to patch the kernel at runtime. Cooler heads prevailed. The point is our software did an ugly hack in order to work, and then Microsoft did an even crazier, uglier hack so that we'd keep working. For years after, when meeting Microsoft engineers at conferences, they'd love to yell at me. When Vista came along, they added signing of kernel models, putting an end to such nonsense, but also providing a real documented API we could use.