Security expert Dan Melamed discovered a critical vulnerability in Facebook platform that allow an attacker to take complete control over any account. The vulnerability is considered critical because it would allow a hacker to hack potentially any Facebook account. When user makes a claim request for an @hotmail.com email he is taken to a link that appears like this:://www.facebook.com/support/openid/proxy_hotmail?appdata[fbid=a6893043-c686-1aadb8b21026 ”
Source: https://thehackernews.com/2013/07/vulnerability-allows-hacking-facebook.html