http://lkiw4tmbudbr43hbyhm636sarn73vuow77czzohdbqdpjuq3vdzvenyd.onion/article/shawn-webb/2015-12-31/introducing-hardenedbsds-new-binary-updater
To distribute version information to users regarding updates, two options are available: propigation through DNS TXT records or a file containing the version number information is placed in the root of the URL that contains all update packages. Option 1 - DNS DNS TXT records will be used to distribute version information. This allows for bandwidth relief by using existing massively-distributed systems.