Flagstaff Unified School District officials say threats to school safety circulated on social media Friday. FUSD says Flagstaff Police informed them that none of the threats were directed at any of the district’s schools, but spread nationally. Superintendent Michael Penca said in a letter to parents that students alerted them to the threats. When started to receive the notices, they called police immediately to investigate the matter. FUSD has made the Anonymous Alerts app available on all student iPad devices to enable reports of urgent information to school officials anonymously.