SHA1 certificates for secure SSL/TLS communications are deprecated due to known computational vulnerabilities. To ensure secure communications, a forced deprecation sounds reasonable (i.e. refuse to connect to these). That has the side effect that it will lock out many users who are unable to use stronger hashes such as SHA256. However, if a fallback to SHA1 is provided (as Facebook is proposing), everyone will be vulnerable to SHA1 downgrade man-in-the-middle attacks.
What to do?
(Score: 0) by Anonymous Coward on Friday December 11 2015, @11:08PM
Facebook do care about their users, because the number of users affects the valuation of the company. The wrong decision here could lead to a drop in Facebook's monthly unique visitors. Even if investors understand the reason for the decrease, the stock price might suffer.