Just a tip: I find it nice to setup my linux box to support the rdate protocol. then rdate <server_hostname>, if the server is in /etc/hosts, or rdate <serverip> otherwise.
To setup an rdate server, use xinetd. It supports the original
RFC868 protocol for serving time, supported by nearly all vintage UNIX systems.
Instructions that work on my Debian server
are here.
Security issues? Not really. It's not more or less secure than NTP, which is unencrypted over the wire. It may be less accurate, but who cares about milliseconds?