A Christchurch company which helps to stop pupils accessing inappropriate internet sites during school hours is now operating in about 300 schools.
Michelle Polglase from Linewize told Nine to Noon research showed more than a third of high school students had tried to use a virtual private network to bypass their school's internet filtering.
Ms Polglas said the problem arose from kids turning up at school with smartphones which could be programmed to bypass the internet filtering systems.
She said Linewize took an innovative approach to blocking the inappropriate content using what's called machine learning.
Ms Polglase said that was able to identify unusual patterns of behaviour, for example a large cluster of kids accessing one particular virtual private network to bypass the internet filtering.
LineWize could also provide tools to allow teachers to control which sites students were on during class.
"For example, in a classroom situation, a teacher can restrict internet access so can let one person be on Facebook or one on Youtube or block it completely for that [particular] class group.
"We do also provide reporting, so if students are attempting to access porn sites or attempting to do risky dodgy things online we do have some visibility over that activity."
However, Ms Polglase said trying to shut down the virtual private networks was like a game of Whack A Mole as they just kept popping up elsewhere.