Local Hostname -- Already in use ... changed. Should I be worried?

Yesterday I came home and woke up my sleeping computer to find a message:

"This computer's local hostname "my computer's name-5.local" is already in use on this network. The name has been changed to "my computer's name-6.local".

To change the local hostname, open System Preferences and click Sharing, then click "edit""

I have no idea what this message means, what is going on with my network, what a local hostname is, and if I should be worried.

Obviously this change has taken place now 6 times.

I'm using the wireless router from my cable company and just did the basic install on it.

Any ideas?

Thanks