I'm reminded of the darpa project I think HD Moore worked on to test new grant paperwork, was basically a wardialler on speed built for about 50$ that could call every number in a given country in less than an hour. There was some amusing speculation about how many bombs in development one could set off by hitting cell phone triggers early. How long semi-random country wide cell phone calls would terrorists stand before abandoning that trigger method.
Other than maybe toying with that, there really isn't much a hacker could do to truly damage an organization like ISIS without discretely handing data over to authorities and letting them make the judgement call.
Even something 'big' but misguided like announcing the locations of ammo depots and training groups could easily, and likely, turn into a case of 'we already knew about that, and thanks for giving the terrorists a heads up when we had an OP planned in three days when a high value target would have been inspecting the camp, yup, real helpful anon'.
People like anonymous dont realize that in a true information warefare its impossible to be an independent and successful third party. If you could there would be literally ZERO reason for the CIA/NSA to work with the GHQ on ANYTHING. In an information war if you have an enemy, you HAVE to side with your enemy's enemies or else you simply risk helping your enemy instead. At least, if you plan to take objectable action with the data you gain.
