On the subject of ntp here for those who are truly concerned about this but would still like to actually have their time updated there are plenty of public NTP servers around you could install the NTP package and use those, or there is always the ntp pool if you don't feel like selecting servers independently yourself http://www.pool.ntp.org/
The latter are all volunteer servers which donate their services to the pool which has some several million users, I actually run two pool servers myself and it is not unusual to see 100,000 active clients on each of those on their own.
Here is a basic NTP config file which will suffice for using the pool those you might want to change the addresses to your local country zone, there is more information on the pool website
Code:
# --- GENERAL CONFIGURATION ---
server pool.ntp.org
server 1.pool.ntp.org
server 2.pool.ntp.org
server 3.pool.ntp.org
# Drift file.
driftfile /etc/ntp/drift
If you want to restrict access to your NTP server then you will want to add some restrict statements, I'll include a few examples but you should change the addresses to match your own setup. Note: If you are behind NAT then this is not necessary unless you are running on a machine configured as DMZ or with port 123 UDP forwarded to it.
Code:
# If you only have the one computer and NTP is running on the same machine then you can just have a default ignore statement.
restrict default igonre
Code:
# If you have several machines on a LAN then I'd suggest the following:
restrict default ignore
# Permit hosts on network 192.168.0.0 with netmask 255.255.255.0 change these if your network is different.
restrict 192.168.0.0 mask 255.255.255.0 nomodify
Then just change the pool server addresses in the configuration files of your other machines to server <your main server ip>
IPv6 address ranges can be permitted the same way, if anyone has any issues I am on the pool mailing list as are a bunch of other helpful people.
Hope that helps.