How secure using Nagios?

Hello Experts,

I have my windows servers located at different data-centers across US and I am monitoring all of them using Nagios server configured on a CentOS. All communications are done via public IP address and I doubt it can invite some security threats too. Can anyone let me know if it is already secure or there some additional security measures which I need to take care to make the entire operations more secure?
Any help would be appreciable.

Thanks,
Denor