What is going on?

I'm also experiencing the popups with the other people. Except mine are videos. One said





"DON'T ♥♥♥♥ WITH ME"





Another one was



"DECEMBER 25TH 2016" and some Japenese stuff.





I haven't been on a server since last year and I haven't downloaded any addons recently.



I've just been doing single player.