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Otago teenagers still largely think a lapse in internet security "won't happen to them" and sometimes suffer the consequences of posting personal information on the 'net.
A survey of 1700 secondary school pupils by the independent, non-profit internet safety education organisation Netsafe found half had posted sensitive information about themselves on publicly available web pages and mobile phone chat rooms without thinking of the possible consequences.
University of Otago media and communications lecturer Dr Erika Pearson said young people were becoming more aware that posting personal information such as their mobile phone number, home address and email address online was unsafe, but many made the mistake of putting online personal photos of themselves.
"They think it won't happen to them. They may not have their address posted, but they will have a photo of themselves outside their flat, so people will still know where they live."
Last year, some students at the university got a fright when the networks of university internet service providers "crossed" and personal information became freely available, she said.
"When people are on the internet they think it is like talking to friends in your bedroom, but it is actually more like talking to your friends in a crowded cafe where people are eavesdropping, either deliberately or because they can't help but hear."
People needed to realise that online was a public space and although there might be rules of "etiquette" on social networking sites, such as not posting photos of others in awkward situations, not everyone obeyed them.
Netsafe research manager John Fenaughty said once information was posted publicly online, people lost control of it.
"You can't control who sees it, copies it, forwards it or who potentially uses it against you. Even if you take it down, there's absolutely no guarantee it hasn't already been copied and posted elsewhere."
The posting of contact details also left teenagers vulnerable to cyberbullying, Mr Fenaughty said.
Another concern was how sensitive information could be accessed by potential employers once it was publicly available.
"NetSafe is already aware of employers who search online to find out information about new applicants.
If their public digital footprint shows applicants in a way that the organisation feels is negative, then they will be unsuccessful."
Otago Secondary Principals Association chairman and Kaikorai Valley College principal Philip Craigie said most schools in Otago talked to their pupils about bullying.
At his school they had also spoken to parents about cyber safety.
It was difficult to control what happened in pupils' private lives, but pupils were alerted to the "inherent dangers" of the internet, cellphone bullying and face-to-face bullying, he said.
Otago Primary Principals Association president Steve Hayward agreed, saying primary schools had cyber safety under control in most cases, with pupils often signing agreements at the start of the year, but teachers could not control what went on in people's homes.