After responsing to com2us, that I will change my game title and informing them, that the phrase "Tower Defense" is descriptive, I got another response from them:

------------------ [...]
Under the Lanham Act – the federal statute governing U.S. trademark matters- a certificate of registration of a trademark upon the principal registration is prima facie evidence of the evidence and registration of the registered mark, of the registrant’s ownership of the mark, and of the registrant’s exclusive right to use the registered mark in commerce on or in connection with the goods or services specified in the certificate. See OMEGA, S.A. v. S&N Jewelry Inc. 1992 WL 142746 (S.D.N.Y. June 8, 1992). In other words, our company’s TOWER DEFENSE mark would be presumed valid unless you have produced in the U.S. court a huge amount of evidence to prove TOWER DEFENSE is a merely descriptive or generic mark.



Further, we have enforced against games provided under the identical or similar name of “TOWER DEFENSE” mark since the registration of “TOWER DEFENSE” mark - particularly in App store and Google Play market. In fact, App Store has denied the submission of any games that adopt the title confusingly similar to TOWER DEFENSE mark. Unlike App store, Google Play market has no pre-examination procedure to prevent trademark infringement. However, we are regularly monitoring games infringing our company’s trademark rights and immediately letting Google to take down such games. At this time, we directly contact with you because it would give you an opportunity to voluntarily take measures for avoiding trademark infringement before Google takes down the games. [...]
------------------

There is no need for huge amount of evidence that "Tower Defense" does describe a genre/type of games. Even wikipedia describes it just like that and the phrase is well known for decades all around the world.

Point is, they got the trademark as long as noone will sue them and driving it invalid. Which would be pretty easy if you can effort the time and money to do so.

com2us know both facts for sure.

So it is very possible that such unethical fool practise will be the default in the future. Everyone is registering stupid trademarks of descriptive words.

In europe I would maybe sue them, because I live there and it would be easier to control. In US .. na .. another one from the US have to do it. I have renamed my game already to avoid any legal actions.

So I really hope, they send their letter to the wrong guy and lose so much money that they have to close their doors.