org-ctrl-k-protect-subtree

org-ctrl-k-protect-subtree is a variable defined in `org.el'.
Its value is

nil

Documentation:
Non-nil means, do not delete a hidden subtree with C-k.
When set to the symbol `error', simply throw an error when C-k is
used to kill (part-of) a headline that has hidden text behind it.
Any other non-nil value will result in a query to the user, if it is
OK to kill that hidden subtree. When nil, kill without remorse.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.1 of Emacs.