Social apps harvesting smartphone details without consent

Twitter has admitted copying entire address books from smartphones and storing the data on its servers, often without customers’ knowledge.

Access to the address book is enabled when users click on the "Find Friends" feature on smartphone apps.

Two US congressmen have written to Apple asking why the firm allows the practice on its iPhone, as it contravenes app developer guidelines.

Twitter has said it will update its privacy policy to be more explicit.

The practice came to light when an app developer in Singapore noticed that his contacts had been copied from his iPhone address book without his consent by a social network called Path.

Dave Morin, CEO of Path, apologised and said Path would ask users to opt in to share their contact information.

However, he noted separately that it was an "industry best practice" to upload or import address book information.

iPhone apps by social sites including Facebook, FourSquare, Instagram, Foodspotting and Yelp are also reported to access the address book.

However, Facebook has told the BBC that its app will only upload address information if the user opts to sync their contacts with the website.

Critics have noted that these apps are all available for download from Apple’s iTunes store, even though the practice of copying address book contacts without prior consent appears to violate its user guidelines.

Social networks have said that data taken from smartphones – which includes names, phone numbers and email addresses – is used only to identify friends who used the same service, and notify the user.

Twitter said it would update its app in the wake of the disclosure, and clarify its privacy policy for users.