The latest incident happened around 6:40 a.m. Wednesday, Sept. 11, at Kellenberg Memorial High School in Uniondale.
An anonymous person sent a message through a crisis chat message system that bombs had been placed around the school grounds, according to Nassau County Police.
The school was cleared with negative results and reopened to students and faculty.
Homeland Security responded to the scene.
The investigation is ongoing.
Click here to follow Daily Voice Patchogue-Medford and receive free news updates.