I would like to warn you about the risk of playing the NK games on the unofficial servers:
It is possible to find NK games on some unofficial servers, but when you play them, it can damage your saved data!
For example, if you play Bloons TD 5 on some website where they have an older version of the game that doesn't have a Jungle track implemented, you can lose your medals earned on the track. You can also find BTD5 versions on the internet that don't have a co-op mode implemented at all, or even specialty buildings, and it can be very unpleasant to lose all your co-op medals or specialty buildings. You can also lose a progress in some achievement, if the achievement isn't implemented in the older version of the game you played.
BTW, you can lose your saved data, even if you don't play the game, and you just go to the main screen of the game.