These phone apps have got your number

The apps, which include Truecaller, Sync.me and CM Security, ask users to upload their phone's contact lists when they install them. That means they end up with huge databases - one app claims to have two billion numbers while another claims more than a billion.

The security blogger Graham Cluley, whose mobile number is stored by one of the apps, says everyone needs to be more careful about what they share: "If you upload your address book, you're not just putting your own privacy at risk - but the privacy of everybody else in that address book.