The best theory I've heard about the authors motivations is that after knocking Krebs offline, with a world record dos, they wanted to muddy the waters a little

The best theory I've heard about the authors motivations is that after knocking Krebs offline, with a world record dos, they wanted to muddy the waters a little. By releasing the source code and letting everyone else fight for control of the botnet, it would be much harder for anyone to trace the original attack back to them.