[Mashiro]

Hacking the DNS of a domain is possible if a) the DNS hosting provider gets hacked (security holes in their system maybe, etc...), b) the account that holds the domain gets hacked somehow or c) maybe someone wasn't careful enough and left access open to an API for the DNS hosting and someone found out and used API access to modify records. Otherwise it would be impossible to simply go and change the DNS entry of a domain. I mean the chance that someone went so far is unlikely.

I could great domains and all point them to your IP if I really wanted. Nothing stops me from doing so. Before you other people owned that IP address and probably hosted sites.