An explosion of people checking into social networks is being exploited by mobile application makers and private detectives, who say they can use people's online chatter and photos to track them and find out where they live.
In March, Apple stopped downloads of a " stalker" mobile application that told men where women around them were "hanging out", using only publicly available information from social networks.
But other readily available apps can do the same and more, say online investigators who use them.
When a person uses a mobile phone to post a tweet on Twitter or upload a photo to the image-hosting website Flickr, sometimes so-called geolocation data can be found lurking underneath the tweet or photo. This can be used to track down their local haunts, including their home or where they study.
"It is quite easy sometimes to work out which house a tweet is coming from," said Neil Smith, a former police officer turned online researcher in Britain.
Geolocation research is a fast evolving area as most applications are built on the back of freely available open-source software.
One of Smith's favourite applications was developed by 27-year-old Greek IT engineer Ioannis Kakavas, who aptly called his invention Creepy.
The free app collates geolocation data attached to a person's tweets and pictures to figure out where they might work, said Smith, who says he uses it to track down perpetrators of insurance fraud for corporate clients.
Police officers in Vancouver, Canada and in Arizona and Colorado in the United States also say they have used Creepy in their investigations.
An array of social networks like Twitter, Foursquare, Twitpic, Flickr, YFrog, Gowalla, and Lockerz can provide such geolocation data, Kakavas said.
Some of these websites allow users to disable geolocation, but those like Foursquare and Gowalla depend on it. Twitter users can choose to enable it when they join and Facebook says it strips off the location data on photos.
Smith, who says he has recently been hired by journalists who want to use geolocation data in their research, says his work is for "honourable, legal purposes".
For many parents, mobile apps that use geolocation can also be a source of reassurance: FamilyTracker and Life360 are two apps which show parents where their children are on a map.
But Smith and other professional snoops admit that many people oblivious to geolocation data can find themselves unwittingly exposed.