Sony showed the Spider-Man: Far From Home trailer at Brazil’s Comic Con, and is reportedly not going to release it generally for another ten days. …Now, generally the MCU has been extremely good at squashing premature leaks before they can even start. But that’s Disney. They have a fearsome reputation in that regard. Sony… does not.
Although, to be fair; you’re more likely to see leaked footage from the convention than a hacked and downloaded trailer.
PS: Details about the movie can be found at the link. Won’t spoil it for you, if you care about that sort of thing.