By the way, a couple weeks ago the Twitter website on my iPhone went haywire, randomly deleting followers and "followings" when I browsed the lists. I restored them manually on a regular PC. I now wonder if this problem could have anything to do with their app, maybe malware associated with it.
Update: Aug. 28
ABC News reports on how difficult it is for Twitter to keep ISIS or similar groups from abusing the service, as there is no central control.