DNS Lookup - Filter "localhost"

This past weekend we started receiving bursts of lookups on our DNS server for "localhost." We blocked our subscriber abusing this lookup (most assuredly malware and not intentional) but curious what safeguards you put in place for DOS attacks on your DNS servers. 1. As an ISP do you see a problem with blocking localhost on your DNS servers? (we don't see any validity to these requests but checking with you to see if we've overlooked something). 2. Do you have an actual localhost zone that issues 127.0.0.1? 3. Do you block >512 Bytes DNS requests? 4. Do you block non-UDP DNS requests or rate-limit requests? 5. Anything else you block/filter on your DNS servers? -=JGR