Try to find some old classic games for the iPhone, such as for example checkers, connect-4, chess, arkanoid, reversi and so on, and you will probably find at least a hundred apps of each. However, try to find a Tetris game for the iPhone. One would think there would be dozens, if not hundreds of apps. You will be surprised.
Why is this so? Because there's a company in Russia called The Tetris Company who claims copyright on the game mechanics of Tetris, and they have been actively sending cease-and-desist letters to all distributors and individuals who provide any kind of Tetris-based game. These letters claim copyright ownership (and nothing else) on the game type and the demand is solely based on that.
The kicker is that copyright does not protect the idea of a game or the method of playing it (For example see this.) Copyright covers the source code, artwork and music of a specific game, but it does not protect the game mechanics themselves. Anybody is free to create their own version of the game with custom code, graphics and sounds.
The copyright claim on the game mechanics of Tetris is completely frivolous and would never stand on court. However, The Tetris Company is is still sending these cease-and-desist demands, and has been doing so for over 12 years.
As noted at that website, if you are distributing your Tetris clone yourself, you can freely ignore any cease-and-desist demand you might receive. The demand has no legal weight, it would not hold up on any court, and The Tetris Company will not pursue it (because they obviously know it would never pass).
However, the situation is very different when you are not the one distributing the game. For example iPhone apps are exclusively distributed by Apple, and as a company Apple obeys cease-and-desist demands automatically without any kind of investigation. In other words, they just leave it up to the author to do whatever he wants. In this case it would require the author to challenge the cease-and-desist on court, and no sane individual is going to go through that trouble, not even if living in the United States, much less if living somewhere else, as the logistics (and cost) involved would be simply prohibitive. (The people at Apple most probably know that the copyright claim is bogus, but they don't want to get involved. I suppose nobody can really blame them for covering their bases.)
The same goes for Android app stores and most other online stores.
What The Tetris Company is doing has no legal basis and could, in fact, be considered illegal (abuse of the judiciary system). However, nobody is going to challenge them.
This is colloquially called copyright bullying: They are shutting down any game that copies the Tetris game mechanics by frivolous copyright claims, and abusing the fact that distributors obey cease-and-desist demands automatically without question. And there's little that individual authors can do about it even though this whole activity is outright illegal and an abuse of the copyright system.
Or in other words, they are claiming legal rights that they don't have, and they are pulling it off successfully by abusing the system.
Just another symptom that the entire copyright system needs a serious overhaul.