Linkability at its best. Been saying for years that FB is trying to help establish the single-sign-on for all to access the internet. Thats why every major email and social outlet are demanding you input your phone number and secondary email alongside your existing account info. Eventually this will help the government know who is behind each IP address. No need to keep avoiding the phone number security prompt at the top of FB anymore, they already have it through their acquisiton of whatsApp, what a shame.