L.A. SCHOOLS CLOSE AFTER 'BOMB THREAT'

http://www.latimes.com/local/lanow/la-me-ln-all-lausd-schools-closed-threat-20151215-story.html

Officials have closed all Los Angeles Unified School District campuses Tuesday morning after receiving a "credible threat" of violence involving backpacks and packages left at campuses.

Question: Since when does ISIS signal their attacks ahead of time?