[CentOS] (Centos 5.6) Server Time NTP Facility

Curiously examining some of the blocked IP addresses in the daily
Logwatch report, I notice strange sites attempting to connect to our
servers on port 123 (the time port).

I also notice our servers successfully contacting official time
references centres which are not those sites trying to connect to us. I
notice too the installed time software is listening on every available
IP. I can not identity any options in any configuration files to
turn-off this listening.

Why are unknown sites attempting to connect to our server to, I assume,
sample the time and how does one turn-off the software's listening on
every IP address, including 127.0.0.1 ?

Thanks,

Paul.