As Lysa Myers, my ESET colleague, has noted this breach appears to have occurred between mid-May and July. It was discovered by Equifax on July 29 and the scale is staggering: 143 million people affected, almost half of all adults in the US!
For those wondering how to identify or mitigate problems caused by this breach, Lysa has some good advice. Unfortunately, the response from Equifax has not been exemplary and there are concerns that it might be trying to restrict consumer rights of redress as part of its "help" process (see this Atlantic article and the update below).
For those wondering how such a thing could happen, I suggest "stay tuned" to your favorite cybersecurity news feeds. We have some information already (Equifax may have fallen behind in applying security updates to its Internet-facing Web applications). However, I am sure there will be more details to come.
In the meantime, I leave you with this weird fact: A share of Equifax (EFX) stock was worth about $143 before the breach, which affected 143 million people. It dropped dramatically after news of the breach broke, closing on Friday at $123. That's a drop of more than 13%. Yet all the indications are that preventing the breach sounds could have been as easy as, you guessed it: 1-2-3.
Update: Thanks to Brian Krebs for flagging the change Equifax that made to its breach alert page. This makes it clear that "the arbitration clause and class action waiver included in the Equifax and TrustedID Premier terms of use does not apply to this cybersecurity incident."
I am providing the address of the breach alert page below, but stress that you use it at your own risk. The fact that I feel compelled to say that is a reflection of how badly, in my opinion, Equifax has been handling the breach response so far: https://www.equifaxsecurity2017.com/
