The Domain Name System is maintained by a distributed database system, which uses the client–server model. The nodes of this database are the name servers. Each domain has at least one authoritative DNS server that publishes information about that domain and the name servers of any domains subordinate to it. The top of the hierarchy is served by the root name servers, the servers to query when looking up (resolving) a TLD.
Edit: emphasis changed
For further actions, you may consider blocking this person and/or reporting abuse
We're a place where coders share, stay up-to-date and grow their careers.
If you lower the TTL DNS servers will have to refetch your entry more often from 'upstream'. So getting the address could take a little longer.
From Wikipedia
Edit: emphasis changed