> is disabling “set date and time automatically” in Software Preferences enough to ensure that ntpd is not running?

**Yes**.

Here is the way to insure yourself of this.
Open a `Termonal` or `xterm` window.
Run the following command:
    ps ax | grep ntp
and notice that you have an `ntpd` process running.

Open `System Preferences` and
turn off `Set date and time automatically:`

Check with the `ps` command above that you don't have any `ntpd` process running.
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> In doubt I might use these instructions to limit the scope

**No**.

This receipe will live you with a running `ntpd` and hence exposed to an attack.