George Duke-Cohan, 19, emailed thousands of schools in the UK with a bomb threat in March, Luton Crown Court had heard.
He was arrested just days later but while still under investigation, he sent more email threats to British and US schools, claiming a pipe bomb had been planted on their premises.
His calls led to the evacuation of more than 400 British schools.
He was arrested again but after being released on bail Duke-Cohan caused havoc at San Francisco Airport with a call claiming a US-bound flight had been hijacked.
“His actions and complete lack of regard for other people caused widespread and unnecessary worry,” said Anne McCracken of the Crown Prosecution Service (CPS). She added in a statement that Duke-Cohan had made the calls “in the hope of notoriety.”
Duke-Cohan pleaded guilty to three offences of making bomb threats. (Reporting by Amy O'Brien; editing by Stephen Addison)
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