Some 24,000 threatening emails were allegedly sent, resulting in around 400 schools being put on alert or being evacuated.
A man has been arrested after thousands of threatening emails were sent to schools and colleges in the UK.
The 19-year-old was arrested in Watford on suspicion of blackmail and making malicious communications relating to the hoax bomb threat that closed hundreds of UK schools this week.
The National Crime Agency confirmed the arrest and said: "We understand parents' and teachers' concerns but stress there was no credible threat to the emails schools received.
"However, we are taking the communications extremely seriously."
The arrest comes after 24,000 threatening emails were allegedly sent, resulting in around 400 schools being put on alert or being evacuated.
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Parents were told to collect their children after what police had described as a "bomb hoax".
Police later said there were not believed to be any viable threats.