Facebook has found an innovative way to encourage use of its email service: reach into users' mobile phone address books and change the email addresses stored against each contact to their Facebook email account.

It has emerged that Facebook's war on competing services now extends beyond the manipulated Timeline and into punters' pockets. The social network's mobile app appears to be altering address book entries to direct messages to Facebook mail accounts. A user composing an email on his or her phone will send the missive to a Facebook inbox the recipient has probably never looked at, and as the original email address is overwritten there's no alternative.

According to reports, address books on iOS and Android devices are being updated by the Facebook app whenever there's an entry in the address book linked to a Facebook account. In some cases it seems the @facebook.com address is being appended to the contact details, but other users are reporting that it's being overwritten too.

Some punters, such as Sam Bibble, found new and separate entries for each of his Facebook contacts, leading to duplication - but at least he didn't lose the original email addresses.

There are also reports of email messages disappearing entirely - but Facebook tells us that such messages have probably ended up filed in the "Other" category which becomes available when one clicks on "Messages" at the left of one's Facebook home. That doesn't alter the fact that data on users' handsets (their friends' preferred email addresses) has been deleted without warning.

Facebook tells us its engineers are looking into it, and they'll let us have more details when they come in. We've had no reports of UK users suffering the same plight, but it might be wise to remove the Facebook app for a while anyway, just until the situation becomes clear. ®