The issue was highlighted in Dunedin last week when several city people had photos stolen from their Facebook pages by internet "trolls", who threatened to post the images of the victims' children on a child pornography site.
The trolls - people who deliberately make inflammatory posts to upset others or are looking for scamming opportunities - and the victims were members of a group set up on Facebook for Dunedin people to trade second-hand goods.
The trolls and several hundred Facebook profiles believed to be fake were removed from the group by its moderators at the weekend and new guidelines put in place for those using the site.
New Zealand Police electronic crime group national manager Maarten Kleinjtes said it was almost impossible for police to track trolls operating in social media, because they could be anywhere in the world and had the ability to change identities and online locations quickly.
"It's like a needle in a haystack."
The best way to deal with the issue, he said, was for those using social media to prevent themselves becoming victims by ensuring they knew how to stop their personal information being seen and openly accessed.
"These are the joys of being connected to the internet.
"Previously, we only had to worry about crooks we met here. Now, we have to be worried [about] crooks all over the world."
Dunedin social media specialist Andrew Long, founder of knowsocialmedia.com, said trolls had been around for more than 20 years, but as social media became more integrated there was a greater need for individuals and organisations to be aware of security, privacy, policies and guidelines for its use, and to spend time ensuring their privacy was protected.
"People just have to think about whether they really want the whole world to see their stuff."
Usually, trolls just posted comments to try to provoke other group members, but the Dunedin case sounded particularly nasty, he said.
People wanting to create a group or online community needed to establish guidelines for use of the group, including what could be expected if guidelines were breached.
People wanting to share online a lot of details about their lives should probably use a pseudonym, he said.
Mr Kleintjes said people, in the first instance, should protect themselves.
He said social media sites such as Facebook usually removed trouble-makers fairly swiftly, but if people had become victims of trolls and did not know what to do, they should contact police.
