Every so often, you need to send Ctrl+Alt+Del to a Windows terminal session. Blindly hitting those keys with the actived terminal window, however, will bring up the Windows Security window (the "Ctrl+Alt+Del Window") of your local machine, not that of the remote machine. My usual reaction in those cases used to be cursing Microsoft for their lack of consideration and giving up in disgust.
No more, though: some time ago, a colleague whose name has disappeared in the recesses of my mind showed me how to do this: press Ctrl+Alt+End. It's probably no coincidence that the "End" key is located just to the right of the "Del" key on a traditional keyboard layout.