Wow. This is disgusting. From Wired:
The nonprofit Epilepsy Foundation, which runs the forum, briefly closed the site Sunday to purge the offending messages and to boost security.
"We are seeing people affected," says Ken Lowenberg, senior director of web and print publishing at the Epilepsy Foundation. "It's fortunately only a handful. It's possible that people are just not reporting yet -- people affected by it may not be coming back to the forum so fast."
The incident, possibly the first computer attack to inflict physical harm on the victims, began Saturday, March 22, when attackers used a script to post hundreds of messages embedded with flashing animated gifs.
Circumstantial evidence suggests the attack was the work of members of Anonymous, an informal collective of griefers best known for their recent war on the Church of Scientology. The first flurry of posts on the epilepsy forum referenced the site EBaumsWorld, which is much hated by Anonymous. And forum members claim they found a message board thread -- since deleted -- planning the attack at 7chan.org, a group stronghold.