They pass around your private information and manipulate your attention so they can sell it. Yet still we spend hours a day on the world's biggest social media platforms - but should we? This Herald series explains exactly what's at stake when you like your friend's Facebook post, Google symptoms when you're sick and share fake news.
Last month, an 11-year-old New Zealand girl received a message from a stranger through a social media site.
Within a day, she had sent the stranger, who was believed to be overseas, a sexualised image of herself.
She was then asked for more images, and was threatened when she didn't comply.
Her parents went to police, who referred it to the Online Child Exploitation Across New Zealand (Oceanz) unit in Wellington.
"Unfortunately it's not that uncommon," said Detective Senior Sergeant John Michael, who heads the six-person team in Wellington. They deal with two or three similar cases a week.
The anonymity of social media platforms and the absence of verification requirements means they are a haven for predators, and easy for vulnerable young people to sign up.
The offender has not yet been caught. Offline, they might have taken months or years to find, groom and exploit a young person. In the case of the 11-year-old girl, it took around 24 hours.
"Could they have approached children otherwise?" Michael said. "I think they would have had a lot more difficulty doing it."
He did not want to name the social media platform in this case - New Zealand police want to keep them onside - but it was one of the major social media companies with more than 150 million users worldwide.
The rise of such platforms, which often ignored police requests for co-operation, had made Oceanz' job more difficult, he said.
"If we look at the reports of suspected online child abuse of children, there were 3000 reports [globally] in 1998," Michael said. "If you jump to 2018, that number has jumped to 18.4 million."
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While child exploitation is at the extreme end of the risks created by social media, the case highlights how the online world can feel like a minefield for parents.
Young New Zealanders are spending several hours a day on social media platforms, where harassment and obsession over body image can follow them home. Harmful images and content are easy to come by and difficult to get rid of.
And in the past 10 years the rise of social media has coincided with a youth mental health crisis - though researchers stress they are yet to confirm a concrete link between the two.
Reports by young people to New Zealand's internet watchdog Netsafe rose 40 per cent in the past three years, and reports related to "personal harm" rose by 85 per cent. Among the most common complaints were "social aggression" and "sexual exploitation".
Social concern about Facebook, Instagram, Snapchat and other online platforms has led to ambitious reforms in Britain, which plans to start requiring social media companies to protect young people and penalise them if they fail to do so.
So should New Zealand - where levels of social media engagement are comparable to Britain - follow suit? And what do the experts say about keeping your kids safe online?
Chris Hollis, a professor of child and adolescent psychiatry at the University of Nottingham, said it has been shown that young people who are depressed spend more time on social media.
And excessive use of social media - more than five hours a day - has been linked to increased distress or anxiety.
But, crucially, no firm connection has been made between social media use and poorer mental health.
"There's definitely a relationship between the two," said Hollis, who visited New Zealand to speak to regulators and academics last month. "But we can't make conclusive recommendations about the causation. We clearly see that there's an association, a link, but in terms of the mechanism, it's too early to say."
In some cases, social media has not created new problems for young people but has amplified existing ones.
Young people who are vulnerable offline are generally more at risk online. This is particularly true in the case of bullying, harassment, and anxiety about self-esteem or body image.
"There is no real boundary," said Hollis. "In the past you could retreat into your own environment and escape - out of school or wherever, and home to your bedroom. This is 24/7, no escape."
Another way social media can amplify offline problems is through what is known as "persuasive design", or techniques which encourage addictive behaviour. The best-known persuasive design is collecting "likes" on content shared on Facebook or Instagram.
"It's a mechanism which is used obviously for advertising and the algorithms that support that, and once you look for things you get more of them in that area," Hollis said.
"It might be searching for information about depression or feeling low, and then they find out that the information is directing them to more negative behaviour, ways of committing suicide or losing weight."
Overseas, psychologists have lobbied tech companies to improve their algorithms so people who search for "self-harm" are directed to help-lines or support. Companies have already done this for people who search for terrorism-promoting content, directing them instead to information aimed at deradicalisation.
Persuasive design came under scrutiny after the death of British 14-year-old Molly Russell in 2017. Her father said she took her own life after viewing self-harm images on Instagram and other sites, some of which had been "suggested" for viewing by the sites' algorithms.
Russell's death prompted British newspaper the Daily Telegraph to run a "Duty of Care" campaign, which demanded regulation of social media companies.
In a major victory for the Telegraph, the British Government plans to give the communications regulator OfCom power to enforce a duty of care on tech companies to protect users from harmful content such as terrorism or child abuse. Companies who don't comply will be heavily penalised.
New Zealand's Internal Affairs Minister, Tracey Martin, said she was keeping a close eye on the British law change. But while she is progressing legislation to restrict access to online pornography, she had no plan at this stage to extend protections to social media.
She said broader internet regulation could depend on the outcome of Justice Minister Andrew Little's work on hate speech.
"Andrew's work will eventually inform where the country wants to sit, where people believe the lines are, and where responsibilities lie."
Martin believed social media companies were now taking more responsibility for their content and protections - partly because of the scrutiny which was placed on Facebook after the Christchurch mosque attacks last year.
Netsafe chief executive Martin Cocker said the British crackdown on social media companies would not work in this country.
"The UK is a big market and it has more weight to throw around internationally. New Zealand is a small country from the Pacific, we … can't demand and say 'If you want access to our market you will behave this way or we'll stop you'."
Instead, New Zealand had to rely more heavily on the goodwill of the big players within the tech industry, he said.
"New Zealand does this well. We did this well with the Harmful Digital Communications Act, it did it well after the Christchurch attacks with the Christchurch Call. This is the model that works for New Zealand - it's more diplomacy than demands."
One of Netsafe's options was to ask social media companies to remove offensive content. When it involved nude images, the companies usually complied within an hour or two, Cocker said. Harassment or bullying takedown requests usually took a day or two.
So how do parents combat this social media minefield?
Associate professor Kerry Gibson, from the University of Auckland's School of Psychology, said it was important for parents to take a balanced approach when discussing social media with their children.
Social media had been shown to have significant benefits for young people, in particular for introverted or marginalised youths - for example, a young gay person who was coming to terms with their sexuality.
Gibson said the stress caused by social media also needed to be seen in context.
"Young people in New Zealand face many other challenges in their everyday lives including poverty, discrimination and bullying. These problems may play out on social media but we need to be careful that we do not distract ourselves from these real-life pressures by simply blaming the messenger."
Parents often assumed their children were naive to the risks of social media, GIbson said.
"My research shows that some young people are much more careful and sensitive in the way that they talk to one another online than adults might imagine.
"Of course this may be less applicable to young people who are new to social media and it would be important to educate this group about the risks of social media and how to protect themselves online."
Kelly Cha, a 16-year-old Aucklander, said she managed her privacy on social media by setting up three separate Instagram profiles.
"My first account is my public account, and it's basically just my basic attributes and what I feel comfortable showing to a stranger," said Cha, who is a member of Netsafe's Youth Action Squad and gives advice to her peers on online safety.
"My private account is for my closest friends, a little bubble of people I can depend and rely on and trust."
She also had a third account which she managed with friends and used to anonymously check out people on Instagram to decide whether to give them access to their private pages.
"Most of my peers are now doing it," she said of the multiple accounts. "Because it's kind of uncomfortable thinking that people might know me inside out."
Cha, who gives advice to young people about online safety, said she previously spent around five hours a day online before cutting that back to three hours.
"I was sleeping a lot less when I was spending too much time on it. And I feel like it was a lot of stress - because the more you spend, the more you are like looking at how many people are viewing my [Instagram] story, and how many people are liking, and how many followers I am getting, why have I dropped followers? It's a lot of extra things that I don't need to deal with and I'm putting it on to myself."
Bhajanpreet Singh, 18, who is also a member of the Netsafe group, said he had witnessed a case at school where social media appeared to have worsened the bullying of a vulnerable student.
"It was some really, really nasty stuff, where they create meme pages to thrash and beat up students online.
"I think social media made it much easier, because you can just sign up and there's no questions asked. That person already had those [self-harm] thoughts, but it could have amplified the situation."
Most of the online problems which the Youth Action Squad heard about were more subtle.
Sarisha Claasseen, 18, said one of the most common concerns she heard was people setting up anonymous accounts in an attempt to elicit personal information or gossip from their peers.
She said it was at the "mild" end of online harm, but could be difficult for young people to deal with because it did not appear serious enough to make a formal complaint but still took an emotional toll.
"It just sticks in the back of your head," she said.
NAVIGATING THE DIGITAL MINEFIELD - TIPS FOR PARENTS
1. Understand - read about potential online risks, challenges and sometimes illegal behaviour young people face to understand what may happen.
2. Learn - ask your child about what they do, how they use devices and who they talk to. Check in regularly to see what has changed.
3. Explore - take time yourself to explore the sites, apps and technologies your child uses to improve your knowledge and understand their experience. Start by asking them how their favourite website or device works.
4. Agree - create a family code with your child to agree on what they can do online including sites to visit, appropriate behaviours, privacy settings and limits on time online.
5. Teach - let them know the basics of online safety, like setting up good passwords, not sharing private information publicly, the permanence of content shared online, not accepting contact from strangers, and being respectful online.
6. Model - be a good example to your child by modelling the sort of behaviours you want to see your child use online and offline. This might mean not having phones at the table or setting limits on use.
7. Plan - make a plan so everybody knows what to do if something goes wrong and where you will be able to get advice. Netsafe offers free and confidential advice, CERT NZ gives practical advice on privacy and security, and when someone is in immediate danger call NZ Police on 111.
• These tips are based on Netsafe's Online Safety Parent Toolkit
Where to get help
Need to talk? 1737 Free call or text 24/7
Lifeline 0800 543 354 (available 24/7)
Suicide Crisis Helpline 0508 828 865 (0508 TAUTOKO) (available 24/7)
Youthline 0800 376 633
Kidsline 0800 543 754 (available 24/7)
Depression helpline 0800 111 757 (available 24/7)
Rainbow Youth (09) 376 4155
Samaritans 0800 726 666
If it is an emergency and you feel you or someone else is at risk, call 111
Australia: Lifeline: 13-11-14
America: Suicide prevention helpline: 1-800-273-8255
UK: 1-800- SUICIDE (1-800-784-2433)
1-800-273-TALK (1-800-273-8255)
• Part One: Big Brother is watching you
• Part Two: Fake News - a threat to democracy?
• Part Three: Kids and social media
• Part Four: How to beat smartphone addiction