Originally it was in the form of a text post, simply telling people to copy it into a file and run it. Later, it was flipped backwards to make it less obvious. The last incarnation was in the form of a .gif image, with a message telling Anon to rename the .gif to .js and run it.
The most effective method was the image attack telling Anon to rename it to .js and run it.
The text of the spam attack
My name is Anonymous. I am a survivor living on the internet. I am broadcasting on all /b/ frequencies. I will be at the page 0 everyday at mid-day, when the GMT timezone reads 12:00. If you are out there... if anyone is out there... I can provide images, I can provide conversation, I can provide companionship. If there's anybody out there... anybody... please. You are not alone.
It is still unknown who has committed this crime and caused the apocalypse of /b/. Was it deluded oldfags, thinking it would eliminate the cancer? Was it one of /b/'s previous victims? Was it one of the other boards? Only the coder knows.