“hackers”, in the “internet hooligan” sense of the term, decided to do something especially disgusting.
They posted tons of links and things on a forum for sufferers of epilepsy. These links and things led to pages with pictures of flashing lights and colours, and whatever it is that sets off pattern-sensitive epileptics.
According to Wired’s article on the topic, this could be the first time that a computer attack has caused physical harm (I suppose that depends on definitions though - I’m sure someone’s gotten a heart attack or something after they lost especially valuable data due to a computer attack).