They re-used all of the art assets, exact level designs, exact name etc. - it's identical. That IS copyrighted material.
Turns out the newgrounds games are embedable, you might not be able to sue them, next time check the portal you upload to.
all they did was using the code bellow now the code can be a iframe embed, a frame etc anything that can pull content from online servers... i don't think they personally host your game.
?<embed src="http://uploads.ungrounded.net/481000\/481558_superstacker2.swf?f1233884077" width="600" height=
"400"></embed>[/code:6j5d0c1d]
The code above is on a public server, all they did was free distributing your game, and added their logo on top before loading. the question is .... is that ethical? no ... but newgrounds gives old flash games free in their feed many of the games there end up on automated arcade script websites like kizi websites or arcadeboosterscripts.
What you can do at this point is update your game version, and lock the game on newgrounds portal. that means any embedding would redirect people to your games page on newgrounds, if you code it that way, or you can simply code it to show a image that is " not child friendly " or something, and then contact them back and ask them about that license if they still want it. have fun.
took me 1 minute to figure the code above... the hard part was finding the game source on newgrounds servers. but is pretty visible inside the newgrounds games page if you right click and show source.
im not usually doing this... im just trying to explain is very simple, they don't host your game on their website they just embed it. so you can unite forces with newgrounds and sue them, if that is against newgrounds rules. problem with suing someone for digital work online, is .... money... is that game worth the thousands of dollars to sue someone in some other country? is it generating that much money that you can afford it? are they making that much money that they can pay damages to your business? what are the damages for them doing that outside moral ones? if you don't have a business around that product/game, even if you instant win in court... your reward from a judge would be like % of the game/product/business generating profit, and the court fees paid by the other party. if not then domain locking is your solution.
Edited: kizi.com which is part of game distribution and all kizi related domains... they are a multi million dollar game distribution network... you will definitely get some nice money from suing them if newgrounds rules are against what they did, and you win in court. However ... they have millions of $ and can keep you in court for years... bankrupting you. [b][i][u]To be understood i don't encourage you to do this[/u][/i][/b], your life will be in a legislation nightmare for some stupid thing for years. just domain lock your games/content.