Understanding Microsoft Hotfix numbers

Question

I got the Microsoft Security Bulletin MS16-008:
https://technet.microsoft.com/library/security/ms16-008
The title names a security update "3124605", so I expected find the hotfix KB3124605 on my system (Windows 8.1), but it's not installed.
The bulletin also refer to the hotfix KB3121212, which actually is installed on my system.

Why are there two different KB numbers for the same thing?

https://support.microsoft.com/kb/3124605
https://support.microsoft.com/kb/3121212

Answer 1

Hotfixes are special-purpose fixes, to solve a specific problem. The security updates solve multiple problems and may include the same fix, but as part of solving a more general problem. For that generality, the latter are better-tested and distributed to a wider audience.

The reason why there are two numbers, of course, is because the fixes are distributed separately, documented in two different places.

Further reading:

• Windows Hotfixes and Updates - How do they work?
• Description of the standard terminology that is used to describe Microsoft software updates
• What's difference between Security Patch, HotFix and Service Pack?
• Best Practices for Applying Service Packs, Hotfixes and Security Patches