Why does Windows require CTRL+ALT+DEL to Logon?

Question

Has Microsoft ever offered an explanation for why they require CTRL+ALT+DEL to login? (Yes I know you can disable it, but it is still their preferred method.) It seems like at one point I heard that it was for security since you knew nothing else could trap CTRL+ALT+DEL, but I've written programs that trap CTRL+ALT+DEL, and it isn't that difficult, so I am pretty sure that was just a myth, either that or the decision to require CTRL+ALT+DEL is based on a fallacy.

Either way, I am curious if there is an official reason, and if that reason has any actual merit.

Thanks!

Before that, it was a well known key sequence for every MS-DOS user — Kevin Panko, Dec 17 '09 at 00:28
How can you trap the ctrl+alt+del key? Even remote desktop or virtual machine softwares cannot do that and must implement an alternative for this — phuclv, Oct 22 '13 at 09:19
This question was re-asked as [What makes Secure Login (CTRL+ALT+DEL) Secure?](http://superuser.com/q/901892/354511), where it got pretty much the same answer. — G-Man Says 'Reinstate Monica', Apr 30 '15 at 21:27

score 9 · Accepted Answer · edited Apr 13 '17 at 12:14

This is the same as this Server Fault question: How does CTRL-ALT-DEL to log in make Windows more secure?.

Here is the accepted answer from there, by Oskar Duveborn:

The Windows (NT) kernel is designed to reserve the notification of this key combination to a single process: Winlogon. So, as long as the Windows installation itself is working as it should - no third party application can respond to this key combination (if it could, it could present a fake logon window and keylog your password ;)

Why does Windows require CTRL+ALT+DEL to Logon?

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