Almost half of all New Zealanders now use online social networks - but most of us are hugely concerned about the information children are sharing on the internet.

A Privacy Commission survey issued today reveals nearly 45 per cent of Kiwis have online profiles - most on Facebook - which is up from 32 per cent last June and 14 per cent in August 2007.

But the rush to social networking coincides with greater concerns over online privacy, especially for children.

Privacy Commissioner Marie Shroff told the Herald a surprising number of people - 57 per cent - believed social networking sites were mostly private spaces.

She said there was an illusion of privacy on sites such as Facebook, Twitter or Flickr, but personal details or pictures could be easily accessed by anyone.

A high percentage of social network users were children, and Ms Shroff encouraged vigilance in protecting them on the internet.

"The internet offers a huge amount in terms of entertainment, education and ability to communicate with others, but there are risks too," she said.

"When children are online they can and do give away a lot of information about themselves, without necessarily being aware of the consequences."

Ms Shroff cited cases of identity theft of children as young as 10 which resulted in online abuse on Facebook.

"[Children] can risk themselves and their families by revealing personal and intimate information, which enables harms such as identity crime, stalking, text bullying and invasion of privacy in various ways."

Last Thursday, 19-year-old Cody Rae Allen of Gisborne pleaded guilty to forgery and criminal harassment after setting up a Facebook page to harass a teenage girl who spurned him.

In a survey by the internet safety organisation Netsafe, 25 per cent of secondary school students said they had been aggressively sexually solicited online.

Children sharing personal details online was the greatest concern among people surveyed by the Privacy Commissioner's office - 88 per cent said they worried about the information their children revealed online.

Seventy-nine per cent were concerned about the security of personal information held by overseas businesses.

Netsafe operations manager Lee Chisholm said any personal information put online should be considered public and permanently accessible.

Even if a user had tight privacy settings on a social network, messages or pictures could be relayed by friends and could resurface years after being posted.

Netsafe had observed some encouraging patterns in children's internet use, she said.

"Young people are quite savvy about keeping knowledge online."

Abuse and harassment did happen, but using social networking sites "is not as big a risk as adults tend to think it is".

The Privacy Commissioner's study found 86 per cent of users said they knew how to protect their privacy by changing settings, and 66 per cent said they had altered their privacy settings.

The commissioner added that internet users should, if necessary, put pressure on internet giants such as Google and Facebook to protect their privacy.

Both sites have been criticised internationally for privacy breaches or not guaranteeing users' safety.

Last month, Ms Shroff wrote a formal complaint to Google after it introduced its Buzz social network.

She accused Google of commercially experimenting on New Zealanders.

Information technology commentator Peter Griffin said privacy rights would be increasingly strained as internet giants tried to make social networks profitable by using targeted advertising.

He cited Facebook chief executive Mark Zuckerberg's recent observation that the age of privacy was over.

Ms Shroff recommended that people could use the resources on internet safety available through Hector's World, Netsafe and the Privacy Commissioner's website.

The privacy survey also showed the organisations most trusted in holding personal information were health service providers, with a 94 per cent confidence rating.

This was followed by the police on 88 per cent, Inland Revenue on 84 per cent and ACC on 68 per cent.

The Law Commission is reviewing the Privacy Act. It says rights to privacy have been challenged by rapid advances in technology.

Net Privacy
* 88 per cent of us are concerned about information that our children share on the internet.

* 43 per cent of us now use a social network site.

* 57 per cent of us think social network sites are private.

* 61 per cent of us are uncomfortable about being targeted by advertisers online.