SYDNEY - An Australian schoolboy who has become an internet sensation after turning on a bully has told how he snapped after years of cruel taunts about his weight.

Casey Heynes, 16, says he has been bullied nearly every day at his school, Chifley College, St Marys, in western Sydney, but could take no more when Year 7 student Ritchard Gale tormented and attacked him last week.

"All I was doing was defending myself. I've never had so much support," he told Australia's A Current Affair TV show last night.

According to Sydney's Sunday Telegraph, Casey revealed he had been targeted by a new group of Year 7 boys, who had started picking on him and teasing him.

The Year 10 student said he found himself surrounded by the students when he went to get a school timetable before class.

As Ritchard backed him against the wall and started throwing punches, Casey said he felt scared and worried that others in the group would also start hitting him.

Eventually, he snapped, picking Ritchard up over his shoulder and throwing him to the ground.

The brawl was recorded on the mobile phone of another student, who later posted the footage online, where Casey has earned "hero" status.

Asked if he was a superhero, he laughed and said: "No, I wish I was."

Casey said his outburst was a "build-up" of more than three years of being attacked verbally and physically by other students.

"They used to slap me on the back of the head and said I was a fatty and to lose some weight.

"I've been duct-taped to a pole before as well. They target me because I don't retaliate.

"I've never reacted that way before but everything built up inside me for three years ... I just had enough. All I wanted is for it to stop."

Casey told A Current Affair he had been bullied almost every day at school and even contemplated suicide a year ago when the taunts became too much.

"I started putting myself down and all the crap just kept piling on," he said. "That's when I contemplated suicide."

The video of his fightback, which the Sunday Telegraph said was taken off YouTube on Tuesday, has gone viral worldwide, spawning dozens of websites and Facebook pages congratulating Casey for fighting back.

Casey said he had been overwhelmed by the number of people who backed him after last week's footage went viral.

"I've never had so much support before," he said. "Nobody touches me and teases me any more."

Both Casey and Ritchard were suspended by the school after the incident, as was the student who filmed it on the cellphone.