A 16-year-old boy has been warned he faces custody after being convicted of sending bomb hoaxes to American Airlines and Delta Air Lines via Twitter.
The teenager, who cannot be named for legal reasons, previously admitted carrying out cyber attacks around the world, including on his local police force and SeaWorld.
He targeted websites in Africa, Asia, Europe and North America from his laptop in the bedroom of his home in Plympton, near Plymouth, Devon.
Devon and Cornwall Police's website was affected for 45 minutes while SeaWorld suffered disruption and a loss of earnings, Plymouth Youth Court heard.
The boy admitted carrying out the denial of service attacks but denied two offences under Section 51 of the Criminal Law Act, relating to bomb hoaxes.
But District Judge Diane Baker found the boy had sent tweets to American Airlines, the White House and Delta Air Lines on February 13 last year.
One posted at 6.46pm to American Airlines read: "One of those lovely Boeing airplanes has a tick, tick, ticking in it. Hurry gentlemen, the clock is ticking."
Another, sent six minutes earlier to Delta Air Lines, read: "There's a nice tick, tick in one of those lovely Boeing planes, high quality."
The judge warned the boy, who has no previous convictions, that he could receive a custodial sentence when he is dealt with later this month.
"You may be a young man but you are a clever young man," she told the teenager, who sat next to his mother in the court.
"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.
"I am aware from the denial of service attacks there was quite a lot of disruption for Devon and Cornwall Police's site.
"There was disruption and loss of earnings in relation to the SeaWorld site.
"It clearly passes the custody threshold and that is something I have to look at."
The boy was charged with the five offences in November and initially admitted the allegations before later insisting he had not tweeted the threats.
He suggested that a remote access trojan (RAT) - in which an attacker controls a computer remotely - could be responsible.
But computer experts found Skype conversations between the boy and an online contact named Whitehat discussing how to carry out the hoaxes.
The judge described Whitehat as "a relatively sophisticated computer operator" who regularly discussed illegal computer misuse.
"I am sure that it was you personally, on the encouragement of Whitehat, who sent both bomb hoaxes," she told the boy.
"You did so knowing how serious such actions would be. The planning involved was both detailed and sophisticated."
The judge adjourned the case until July 20 to allow for reports to be carried out.