Mozilla have an excellent explanation document covering the backdated certs in detail here: https://docs.google.com/document/d/1C6BlmbeQfn4a9zydVi2UvjBG...
(Thanks to @xnyhps for the link in a reply to this comment.)
WoSign, described elsewhere as China's largest certificates authority, are a CA who have been found to have backdated SHA1 ceritificates to work around browser restrictions on SHA1 cert issueances. SHA1 is no longer considered secure. Resolution of that issue is discussed in new mozilla.dev.security.policy Usenet group peered by Google Groups: https://groups.google.com/forum/#!msg/mozilla.dev.security.p...
A better source for WoSign's update to the story is in the PDF posted to the newsgroup, here: https://www.wosign.com/report/WoSign_Incident_Report_Update_...
Titled "WoSign Incidents Report Update". Which is even less descriptive than the title presently given on this HN post, though perhaps what HN posting guidelines prefer. I'll let @dang wrestle his conscience on that one.
In that document are several issues listed, the one relevant to this HN post appears to be:
"9. Issue S: Backdated SHA-1 Certs (January 2016)
"WoSign has issued certificates after January 1st 2016 but backdated the notBefore date to be in December 2015.
This has the effect of avoiding the blocks in browsers regarding SHA-1 certs issued after January 1st 2016. The
number of certs affected is probably 67, but may be a few more or less."
Following down from there, several corporate restructuring steps are mentioned, including:
360’s Corporate Development team has been notified to execute the process to legally separate Wosign and Startcom and to begin executing personnel reassignments. StartCom’s chairman will be Xiaosheng Tan (Chief Security Officer of Qihoo 360). StartCom’s CEO will be Inigo Barreira (formerly GM of StartCom Europe). Richard Wang will be relieved of his duties as CEO of WoSign.
There is background on the story from:
"WoSign Mis-Issued SHA-1 SSL Certificates [Updated]" (August 24, 2016)
"Mozilla Ready to Ban WoSign Certificates for One Year After Shady Behavior" (September 26, 2016)
The second article details Mozilla's issues with WoSign, including purchase of an Israeli CA, StartCom
I'm not claiming anything other than a 15 minute familiarity with the situation here. I may have heard earlier rumblings but really haven't followed this at all and wasn't consciously aware of particulars.