The man's lawyer said the plot was a "jihadi fantasy" and his client knew nothing about it.

The judge ruled that evidence of a terrorist group was "overwhelming". The man is the first person to be found guilty of a terrorist offence in Canada since the country enacted anti-terrorism laws in 2001.

The arrests of the 18 group members made headlines around the world and heightened fears in Canada, where people believe they are relatively immune from terrorist attacks.

Prosecutors said there were plans to truck-bomb nuclear power plants and a building housing Canada's spy services.

Seven of those arrested have since had their charges withdrawn or shelved. The trials of 10 adults, including the alleged ringleaders, have yet to begin.

The young man was the first to go on trial. Superior Court judge John Sproat found him guilty of knowingly participating in a terrorist group.

As the 94-page judgment was handed down, the defendant's mother wept quietly in the back of the court.

The man, 20, has not been identified because he was 17 when he was arrested in 2006. Prosecutors say he attended a training camp where he took part in military exercises and firearms training, and that heknowingly participated in a potentially deadly conspiracy.

He had pleaded not guilty to the terrorism-related charges.

Judge Sproat rejected the defence argument that the plot was a "jihadi fantasy" the defendant knew nothing about.

"He clearly understood the camp was for terrorist purposes," the judge told the court, adding that few would have believed the September 11 attacks in the US were a possibility before they happened. "I'm satisfied beyond a reasonable doubt a terrorist group existed."

Judge Sproat rejected defence arguments that two camps organised by the alleged ringleaders were a religious retreat or recreational in nature. He said participants marched, played paintball games, shot a handgun and heard lectures on waging war against the West.

There was clear evidence that the youth had listened carefully to his mentor, the plot's ringleader, and wanted to please him, and therefore understood what the camps were about, the judge said.

The prosecution's star witness, Mubin Shaikh, had infiltrated and spied on the alleged terror cell members before they were arrested.

He said outside court that the youth should not have been found guilty. Mr Shaikh called the man a "naive Muslim kid who fell into the wrong circle of Muslim kids".

Judge Sproat noted that the defence did not make any suggestion that payments influenced Mr Shaikh's evidence. He said he found Mr Shaikh to be a truthful and reliable witness, a development that does not bode well for the adults in their trials.