And this is Very Wrong (tm):
$ host -t cname -v name-services.com. dns1.name-services.com.
Host name-services.com not found: 3(NXDOMAIN)
In short: for *some* types of records for a valid name, the server
returns NXDOMAIN, which it should not be.
Obviously, when doing this query using a caching nameserver, the
cache gets poisoned (remembering that the domain in question
does not exists, as opposed to "No data of requested type"
Another example for a domain hosted by them: