DynDNS Safe?

[townofnewmarket]

I found a PC using DynDNS on our network. While I understand what it does, should I allow it? We run 3560s and Cisco IP telephony. Not long ago someone plugged in a wireless router which set the network into fits. I am wondering if DynDNS is safe enough to allow. And if not, how would you block it? Reading their website, it seems like it's pretty hard to block if someone has any IT knowledge whatsoever.

Thoughts anyone?

[#2]

You can feel safe using a DynDNS Certified products and know that this product will not have negative effects (such as blocks for abusive updating) on their DynDNS account.