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An 18-year-old man has been arrested after hoax bomb threats were sent to thousands of schools in the UK and US.
The teenager was arrested in Andover in Hampshire on Wednesday on suspicion of making threats to kill, blackmail and malicious communications.
Two other 18-year-olds were arrested in Hertfordshire in March.
The National Crime Agency said the series of threats "caused huge worry and inconvenience" and that the investigation was ongoing.
The agency's senior investigating officer, Marc Horsfall, said: "Anyone thinking that law enforcement doesn't take such offences very seriously should really think again."