Quora

 Quora  is a question and answer hosting silo that is unarchived (actively blocks the Internet Archive), and exposed 100+ million users data in December 2018 breach.

Pingback
Quora appears to support sending pingbacks as of 2015-02-06. received a pingback from Quora from a comment someone wrote that included a link to his post. The pingback source was the quora question URL with a fragment ID to the specific comment.



Very Closed
Worth noting: Quora has no public API, no backup/export tools, blocks anonymous display of answers, and banned the Wayback Machine entirely. Andy Baio, https://twitter.com/waxpancake/status/453958676529696769
 * 2018-12-04 Andy Baio: Why You Should Never, Ever Use Quora

2018 User Information Breach
"The compromised information includes users' names, email addresses and encrypted passwords as well as data from social networks like Facebook (FB) and Twitter (TWTR) if people chose to link them to their Quora accounts."
 * 2018-12-03 Quora blog post: Quora Security Update
 * 2018-12-03 CNN: Quora says 100 million users hit by 'malicious' data breach
 * 2018-12-03 The Verge: Quora says hackers stole up to 100 million users’ data
 * 2018-12-03 TechCrunch: Quora says 100 million users may have been affected by data breach
 * 2018-12-04 PCWorld: Quora data breach FAQ: What 100 million hacked users need to know