These offences, between October 2014 and January last year, relate to denial of service attacks on websites in Africa, Asia, Europe and North America.
He denied two offences under Section 51 of the Criminal Law Act in connection with bomb hoaxes made to American Airlines and Delta Air Lines on Twitter.
Giving evidence during the one-day trial, the boy admitted carrying out the attacks on websites including the American marine mammal park and Devon and Cornwall Police.
“A large part of the websites that I had taken down were to do with dolphin hunting,” he told the court.
“I have always been for animal rights and I am really into computers and things so I thought, in protest, and to see what I could do, I would do it.
“I joined up with other people who were doing it. I was fighting for animal rights. I was 14 and 15 then.”
Tweets from an account linked to the teenager were sent to American Airlines, the White House and Delta Air Lines on February 13 last year, the court heard.
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, said: “There’s a nice tick, tick in one of those lovely Boeing planes, high quality.”
Prosecuting, Ben Samples said the FBI was notified of the tweets and senior management at the airlines investigated them. The threats were viewed as “unspecific” and the matter was referred to the UK authorities, with no further action taken by the airlines.
Investigators from the Operation Zephyr Regional Cyber Crime Unit traced the tweets back to a computer in the bedroom of the teenager in Plympton, near Plymouth, Devon.
The boy was charged with the five offences in November and initially admitted the allegations against him 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.
A joint report by experts for the prosecution and the defence found it was “not likely” that his computer had been accessed by a RAT.
The boy told the court: “I feel I could have been stitched up by, I don’t know, but I think I could have been disliked by someone in the past and they have done it to me.”
He admitted sending tweets to the Operation Zephyr Regional Cyber Crime Unit and an email to the investigating police officer following his interviews.
One tweet said: “To be fair they caught me red handed”, while a second added: “I still maintain the utmost respect for Zephyr.”
The email read: “I can’t bear this any longer. I would prefer if you didn’t discuss this with my Mum please.
“I have messed up, I know that and I won’t do anything so stupid ever again.”
It is understood the Devon and Cornwall Police website was affected for 45 minutes following the teenager’s attack on January 26 last year.
District Judge Diane Baker will deliver her verdicts in the case at the court on July 6.