Would you give Facebook your mobile number?

Sarah Coles
Facebook via phone
Facebook via phone

Paul Sakuma/AP/Press Association Images

Facebook has started asking its 900 million users for their mobile phone number. It says it is part of a drive to improve security, because it builds in an extra level of protection for your password.

But why does it need your mobile number for this, and is there any risk that this in itself poses a security risk?