A spate of threats and false reports of shooters have been pouring into schools and colleges across the country for months, raising concerns among law enforcement and elected leaders. Schools in Pennsylvania were the latest targeted by so-called swatting. Computer-generated calls on Wednesday made claims about active shooters, but it was all a hoax. One day earlier, nearly 30 Massachusetts schools received fake threats. School officials are already on edge amid a backdrop of deadly school shootings, the latest Monday at a Christian school in Nashville.