A 16-year-old boy has been found guilty of sending bomb hoax threats to two US airlines through Twitter.
Plymouth’s youth court heard the teenager, who cannot be named, sent messages to Delta Air Lines and American Airlines.
He previously admitted cyber attacks on Florida’s SeaWorld theme park and Devon and Cornwall Police.
Judge Diana Baker told the teenager his planning was “both detailed and sophisticated”.
The court previously heard American Airlines received a threat on Twitter on 13 February 2015 which read: “One of those lovely Boeing airplanes has a tick, tick, ticking in it. Hurry gentlemen, the clock is ticking.”
A similar tweet was also sent to Delta Air Lines on the same day.
The teenager originally pleaded guilty to three offences under Section 3 of the Computer Misuse Act relating to denial of service attacks.
He was found guilty of two offences under the Criminal Law Act relating to the communication of bomb threats.
Judge Baker warned the teenager, who has no previous convictions, he could receive a custodial sentence.
“You may be a young man but you are a clever young man,” she said.
“It is the level of detailed planning, the level of sophistication that there was to hide what had happened and the fact that there were two bomb hoaxes.”
The case has been adjourned until 20 July for sentencing.
No action was taken by the US authorities following an assessment of the credibility of the threat and the matter was passed to the UK authorities.
The teenager had suggested a remote access trojan (RAT) in which an attacker controls a computer remotely could be responsible.
Det Sgt Aled Jones, from the South West Regional Cyber Crime Unit, said: “[The] conviction is the result of a lengthy and wide ranging investigation into the online activities of this individual.”