An Auckland mother has been left distressed after her young daughter's phone repeatedly displayed explicit porn videos and "predatory" sex messages.
And online safety experts have warned all iPhone and Android phone users are at risk of being targeted by malicious malware if the devices are connected to Wi-Fi networks.
The Westmere girl's mother said these images and messages had so disturbed her 12-year-old that she is having trouble sleeping and is spending nights in her parents' room.
A budget new Android phone was bought for her daughter to use for texts and phone calls to keep in touch with family and friends.
Caroline, who asked that her last name not be published to protect her daughter's privacy, said they hadn't bought data because they didn't want her using the internet unsupervised.
At first there was no problem but about six weeks ago her daughter complained that "rude stuff" kept popping up.
It had appeared to have a virus which caused the phone to switch on Wi-Fi and pornographic videos and messages to display.
"Videos would just pop up and start playing full screen," Caroline told the Herald.
"Oh my God, it was really disgusting stuff and the messages were really predatory.
"She has been petrified ever since. We had tried to be so safe by not letting her have data."
The phone had spontaneously turned on Wi-Fi and offensive images appeared while it was being examined by a phone technician.
Caroline had wondered whether cheap Android phones were more susceptible but internet safety group NetSafe said all devices that can link to the internet are at risk.
While the cost of the phone was not a major factor older software may make a device more vulnerable, said chief executive Martin Crocker .
Not having data turned on prevents data from downloading from the telco network but won't protect you from malware if you connect to the Wi-Fi network.
Crocker said there was a lot of malware targeting both android and iPhones.
The chances of malware being in apps installed from Apple and Google stores was "low but not zero", while material downloaded from other sources was riskier.
Problems invariably begin with an action by the user, Crocker said.
"Almost 100 per cent of the time the user needs to be tricked into clicking on something to begin the process.
"Sometimes people will download [malware] thinking, for example, they are getting a game.
"From that point on they may have lost control. It can take just one click and potentially you have a big clean-up job on your hands.
"Once malware has got deeply into an IT device, and especially a phone, it can basically take over.
"And sometimes children will click on downloads without being fully cognisant of what they have done. Or they might not want to tell their parents they have been downloading things because they don't want to get in trouble."
Spam email or a pop-ups on legitimate sites that lead to rogue sites were risk areas.
"The combination of having that link and having a way to download it, such as being on a Wi-Fi network, leads to malware being installed on the phone."
Crocker said parents buying their child's first phone need to recognise that every modern phone has the ability to connect to the internet and the dangers that go with that.
He advises parents to talk to their children about the range of things that could go wrong and have a plan if that happened.
"If porn pops up on your child's phone you want them to realise that can happen and to be comfortable to tell you."
Some devices have parental controls that include the ability to approve apps and set time limits for internet access.