Smartphone users have been warned of privacy dangers as companies are using free apps as 'fronts' to allow them to spy on users' text messages, intercept calls and even track their location.
By accepting little-read terms and conditions when downloading apps, consumers give developers the right to harvest vast swathes of private information.
Facebook insists that people using its Android smartphone app agree to give them permission to read their text messages, although the internet giant said it had not yet taken advantage of this right.
Social media sites Flickr and Yahoo! have also alleged to read text messages via their apps, while apps from smaller companies allow them to extract private details about users' lives. They can even remotely take images from users' handset cameras and even dial their phone and intercept calls without them knowing.
Privacy campaigners criticised the abuse of personal information. Nick Pickles, director of Big Brother Watch, described the apps market as "an unregulated Wild West".
"Your personal information is a precious commodity, and companies will go to great lengths to get their hands on as much of it as possible," the Daily mail quoted Emma Draper, of the Privacy International campaign group as saying.
The Facebook app has been downloaded to Google's Android smartphones more than 100million times, yet few of its users are thought to know that they have agreed to give Facebook the right "to read SMS messages stored on your device or SIM card".
Apps are also used to identify the location of users through global positioning software and access the phone numbers and email addresses of their contacts.
They can also be used to gain information about the app users' web browsing history.
These details are often sold on to advertisers and market research companies, exposing those downloading the apps to unwanted advertising and spam messages.
Daniel Rosenfield, director of app company Sun Products, said selling on the information was far more lucrative than charging for the app.
"The revenue you get from selling your apps doesn't touch the revenue you get from giving your apps away for free and just loading them with advertisements," Rosenfield said.
A spokesman for Facebook said the request for permission to read text messages was to allow the app to read and write data between itself and the phone's SMS feature, rather than for the company to trawl individuals' messages.
"If Facebook ultimately launches any feature that makes use of these permissions, we will ensure that this is accompanied by appropriate guidance," he said.
Google also commented on the app.
"From the beginning, Android has had an industry-leading permissions system which informs consumers what data an app can access and requires users' approval before installation," Google said.