All I know is that a lot of Hackers use that site.
The warning was supposedly posted on the r9k thread
“r9k/ is a forum dedicated to anonymous sharing of personal anecdotes on the image board site 4chan. The /r9k/ community is most well-known for its greentex.”
Its just shocking that someone can post a threat like that and the response from people seemed well, pretty cool with it. If someone posts a threat and I see it I would report it, better to be safe than sorry