Since the splitted DAO (dark DAO) has the exact same vulnerability in its code, is it possible to execute the same attack to the attackers DAO?
That idea may have been part the motivation behind this post:
"Is anyone in the process of splitting from the DAO right now? It would really help if the person whose split will finish in 2 hours (#69) can contact us."
More evidence to support this idea:
Q: "How do we drain? What should I do to try to get my DAO out?"
A: "You cannot do anything. If I got that right, you can only drain (attack) with a finished split proposal (takes min. 7 days). The attack is to then initiate the split in a way that keeps splitting ether without reducing the number of tokens (exploiting a bug in the split code). That's why Vitalik is asking for people with near-finished proposals so they can use one as a counter-attack, to try draining faster than the original attack.
(That is, if the exploit is something like described here: https://blog.slock.it/no-dao-funds-at-risk-following-the-ethereum-smart-contract-recursive-call-bug-discovery-29f482d348b#.2f9e1h8he)
After the incubation period of the new DAO and if you stalk him with DAO tokens I would say:
Yes, you can
Is this an option together with a softfork that mask his DAO tokens as invalid?