Some also have suggested LettersofMarque might be a legal mechanism for such action (which are like a government license to take actions attacking or capturing enemies) or providing an exemption from the CFAA to go after attackers.
Even though Article 1 of the U.S. Constitution allows Congress to issue LettersofMarque, they were forbidden in the 1856 Paris Declaration, which as been accepted as customary international law. (Theodore Richard produced an excellent journal paper on this topic analyzing the use of private security providers for piracy).