At least a dozen U.S.-designated terror groups maintain a presence on Facebook, a review by Bloomberg Businessweek shows. That includes Hamas and Hezbollah in the Middle East, Boko Haram in West Africa, and the Revolutionary Armed Forces of Colombia (FARC). The terror groups are rallying supporters with everything from gruesome photos of death caused by their enemies to quotidian news about social services they offer. Once Facebook kicks these groups off, it doesn’t appear to use sophisticated means to prevent them from coming back. In April nine Hezbollah-related Facebook pages disappeared after the nonprofit Counter Extremism Project publicized links, including a tribute page to martyrs; it had more than 60,000 followers. Within two weeks, a replacement popped up.