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Better yet, don't run your own DNS - 99% of sites shouldn't be running their own DNS servers.
If you've go colocation in multiple U.S. cities, as well as on each continent, run your own DNS servers.
If not, use your registrar, host (but often as poor a choice as running your own), or third-party DNS service.
It's usually free with your registrar, so not sure why so many people insist on running their own, when it's almost always results in inferior performance and problems like this.
change passwords for the domain registrar account AND the email addresses involved.
The OP didn't say who runs their DNS. I'd assumed they are running their own.
Good time to remind everyone to include as many details as possible when describing a problem.
There are many ways of handling DNS, and many ways that somebody might breech security.
So.... details? Just what was hacked?