There was a part in the show where Tyrion told all the people he thought were Cersi's spies a slightly different version of who Mycella would marry. When Cersi confronted him about it, he was able to figure out who had given her the information.
D and D supposedly did this also, and it was a warning to people that they would not communicate anything to the person or fire them, if they deduced who had talked by reading the spoilers getting released. This made a lot of strange stories come out, about what was going to happen, that people absolutely believed in.
Someone spoiled season 8 a couple of weeks before episode one aired, but because it was so hard to tell which plots were true, it kept us guessing. There was a whole discussion about an invasion of others in the Reach for instance, that proved to be nothing but a decent fan fiction.