Facebook says it will fix a software bug that has modified e-mail contacts on users' mobile phones, promising it will be resolved soon.
The bug has caused e-mail details stored on smartphones to be replaced with @facebook.com e-mail addresses. This followed last week's move to make Facebook's own addresses visible by default on its website, hiding the ones originally listed by users.
The bug affected users who activated the Facebook "contact sync" feature on Android and Blackberry phones, according to the Telegraph. It has also beta versions of Microsoft Windows Phone 8 and Apple’s latest operating system iOS6.
Facebook has blamed a bug in a software tool that was designed to ensure that, when users amended their contact details, the changes would be made to their Facebook friends' smartphone address books.
In a statement, the social networking site acknowledged that "for people on certain devices, a bug meant that the device was pulling the last e-mail address added to the account, rather than the primary address, resulting in @facebook.com addresses being pulled".
Because Facebook's synchronisation tool only synchronised e-mail addresses that were visible on its site, and it had made third-party addresses invisible by default, pre-existing contacts were deleted as a result.
Anthony Mullen, senior technology analyst at Forrester, told the BBC: “The gravity of changing personal data on users' phones is much greater than just changing them on a cloud-based service or a website.
"The lesson here is Facebook should have offered a simple wizard walking people through the change, showing what impact it would have, rather than just letting it happen automatically.
"However, despite talk of a backlash it doesn't seem these problems have been grave enough to have motivated users to quit the network.”