4Chan is very loosely defined as an image-pasteboard website, full of content of every imaginable category. Depending on whom you ask, 4Chan is either "the heart and soul of the Internet" or "where integrity goes to die" — a place for celebrity nude photo leaks, gamergate, and endless trolling.
No matter what anyone's personal feelings about what goes on the site's many boards, there's no doubt about its contributions to internet culture. 4Chan brought us lolcats, Chocolate Rain, and RickRolling.
Now the site's humor has a purpose, making fun of the Islamic State (a.k.a.: "Daesh"). This could be bad for an organization whose international recruitment strategy depends so much on the tone of its social media strategy (ISIS, not 4Chan, that is).
See the original 4Chan thread here.