Calif. school closed after Yik Yak threat MANHATTAN BEACH, Calif., Nov. 18 (UPI) -- Threats posted to the mobile app Yik Yak prompted officials to close Mira Costa High School in Manhattan Beach, Calif. Police investigating the messages Tuesday said the threat was "not specific and vague in nature." "If you go to Costa you should watch out very closely at school today," the message posted Monday said. Another message, posted later in the afternoon: "Nice try costa, today was just a drill." Manhattan Beach police confirmed two other messages appeared on the app that referenced the school. "Almost every school shooter has left 'warnings' before they committed their crimes that everyone ignored... it's something to take seriously just remember that," one, posted at 8:31 p.m., said. And 15 minutes later: "Apparently there is a third threat... Tomorrow at 2. be ready, Costa. You're going on lockdown.' Yik Yak is an anonymous app that allows users to post anonymous "yaks" within a 1.5 mile radius. Manhattan Beach Unified School District superintendent Mike Matthews and Costa principal Ben Dale originally planned to keep the school open Tuesday, but later decided to close. "My priority one is the safety of students... we have teaching and learning going on in these classrooms every day, diligently, and so there is always a concern for that and making sure that our instructional program continues," Dale said. But all that comes to a screeching halt when we feel the safety of our students is in jeopardy in any way. Messages posted to Yik Yak have been involved in several incidents near schools, including a bomb threat at nearby San Clemente High School in March and at SUNY Canton in New York in October.