Don't act all surprised that the latest update for the Kindle Fire, version 6.2.1, has already been rooted. That's the way things are with Android tablets and despite its skin, the Kindle Fire is Android at heart. Doubly so, in fact, if you take the time to apply this root to get full access to its inner workings. Android Police and RootzWiki put the hack together and tested with a group of savvy hackers before unveiling it to the world, and it consists of a relatively short series of steps that begins with a custom sideloaded app and ends with complete superuser access.
There's always a good chance that a future update from Amazon will break this root, as the 6.2.1 update itself did with previous methods — but there's an even better chance that the Android community will continue to find ways in.