Knoppix is not doing more then asking the DHCP server for an IP. If you allow that and don't want that, thats your fault.

If you don't want Knoppix to do that use at bootup:

"knoppix nodhcp"

Ok, but this is an issue, which independently of knoppix exists in your network.

So I'd suggest fixing your DHCP server to not create a DNS entry.

And even if Knoppix did (it does not do that) create a DNS entry, you should fix your network and not say:

The program is bad.

I mean if Knoppix could do that, everyone could do that, which does not help your security at all. So prohibiting is no solution.

cu

Fabian