查了一下wikipedia，是这样说的：

http://en.wikipedia.org/wiki/Control-Alt-Delete

Windows NT is designed so that, unless security is already compromised in some other way, only the WinLogon process, a trusted system process, can receive notification of this keystroke combination. This is because the kernel remembers the Process ID of the WinLogon process, and allows only that process to receive the notification. This keystroke combination is thus called the Secure Attention Sequence. A user pressing Control-Alt-Delete can be sure that it is the operating system (specifically the WinLogon process), rather than a third party program, that is responding to the key combination, and that it is therefore safe to enter a password. It was chosen as the secure attention key in Windows (instead of, for example, the System Request key), because on the PC platform no program could reasonably expect to redefine this keystroke combination for its own purposes.

但显然这样的安全是有限的，虽然在登录时候能够对密码提供一定的保护，但若系统已经被做了手脚，密码的安全就无法保证了。所以才有了unless security is already compromised in some other way 这一句。

外一则：

1. 有个乐队叫做Ctrl+Alt+Del, http://en.wikipedia.org/wiki/Ctrl-Alt-Del_(band)
2. 有好几部电影叫做Control Alt Delete
1. http://www.imdb.com/find?s=all&q=Control+Alt+Delete
2. http://en.wikipedia.org/wiki/Control_Alt_Delete_(film) 
3. 有部漫画叫做Ctrl+Alt+Del http://www.ctrlaltdel-online.com/

相关文章：

1. 转载 瘾科学：铁轨的轨距
2. Concentration exercises
3. 2010-03-22 每周Twitter总结