[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.