"With regards to the still photograph incident, which was dealt with last year, I would like to make clear that nothing of a lewd nature was circulated. That however should not lessen the concerns and seriousness of such behaviour," he told the Herald.
He said the school would not stand for such behaviour and that it was working with the students, their families and providing support for those affected.
He said the police and Netsafe were involved.
He added: "We have sent boys to the board of trustees for incidents involving cellphones."
The Herald understands that one boy took an upskirt photo from his personal cellphone.
Another boy filmed a video of a female staff member teaching in the classroom and uploaded it to an internet porn website, it's understood.
Hill denies claims the school has failed to act promptly.
"The first priority has been to protect the wellbeing and interests of victims. I'd refute a delay," he said.
The school has responded by clamping down on cellphone use in the classroom.
In a missive sent to parents and caregivers, seen by the Herald, Hill said the school would no longer allow cellphones to be used in class "unless the boys have had a clear and specific instruction from a teacher".
"The teacher is in control of the classroom," Hill wrote, after telling pupils of the cellphone crackdown during a special assembly.
"This decision has been made after some incidents involving the use of cellphones in class that are contrary to the school values and that do come under the Harmful Digital Communications Act. I am also aware of concerns about a state of continual distraction that some students seem to be under.
"I have been heartened that students have reported the recent incidents to me. This confirms that most of our students have a clear moral code and will take a stand when this is crossed."
Police confirmed this afternoon that it is investigating.
"Christchurch Police can confirm that a complaint has been received and police are working alongside the school to ascertain what has actually occurred and who are involved," said Detective sergeant Daniel Isherwood.
Netsafe, New Zealand's independent, non-profit online safety organisation, said its service under the Harmful Digital Communications Act was confidential and would not confirm whether it had received reports about specific incidents.
Hill has asked parents to talk to their sons about their use of social media and to monitor it, along with their cellphone use in general.
"The underlying purpose of school is that caring adults [teachers] get alongside students and act as high quality role models. This purpose is enabled by a culture of respect," Hill wrote.
"I do hope that students are able to respect the role of the teacher and the school's position on cellphones."
Students will continue to use their school approved devices and the school network in class for the purposes of "enhancing their thinking and engaging with a 21st Century curriculum".
Hill said it was important not to blame cellphones.
"We talk to the boys about being good men, not real men. And let's not blame the devices. Boys, at times, have got things wrong," he said.
"We've got strong values. It's all very well to have the values, but at times you do have to take some action."
It comes as schools around the country wrestle with how to fight inappropriate digital behaviour following an explosion of social media and online bullying.
Numerous incidents have emerged nationwide in recent years of humiliating "sext" pics being sent among friends, trolling and hurtful online posts, and fights filmed on mobile phones then footage uploaded onto Facebook.
Last month, the Weekend Herald reported that Auckland's Kowhai Intermediate is this year asking for its students to cut all links to social media - the likes of Facebook, Instagram and Snapchat - for the two years they attend the school.
Today, Whetu Cormick, president of the New Zealand Principals' Federation, said the "unacceptable behaviour" at CBHS highlights the need for all schools to have clear guidelines on students' use of digital technologies at school.
Digital use policies should be in all schools, he said, with the children, parents, and teachers having discussions around what it means.
"Respect and how we treat other people is one of New Zealand's top values, and in almost every school, a description around the word of respect would sit as one of the school's values. Every year, [pupils] would be reminded what respect looks like," Cormick said.
PPTA, the professional association and union of New Zealand secondary teachers, declined to comment.
