Yahoo has revealed that a hacker or hackers compromised more than a BILLION user accounts.  That's more than double than the number of accounts impacted in the previous biggest online security breach in history - which also happened at Yahoo.

(Note to Millennials:  Yahoo! was an ancient search engine that Grandmas and Grandpas used to utilize to find pages on Geocities via Netscape)

"It's shocking," said internet security expert Avivah Litan of Gartner Inc.

The Sunnyvale, California-based silicon valley pioneer revealed that the breach occurred in in August 2013, more than a year before a separate hack that Yahoo announced nearly three months ago, which affected at least 500 million users.  Until now, it was believed to be the most far-reaching hack.  Today's revelation more than doubles that.

It is not clear if the same hacker or hackers are responsible for both attacks.  The 2014 hack has been blamed on an entity backed by an unidentified foreign government.  Yahoo hasn't been able to identify the source behind the newly announced 2013 intrusion.  In both cases, the ne'er-do-wells stole names, email addresses, phone numbers, birthdates, and security questions and answers.  Yahoo is requiring users to change their passwords, although if you've done so recently you might be okay.

The stolen information has not been posted online.

Yahoo shares fell two percent after the news broke.  It's not clear how this might impact Yahoo's sale to Verizon Communications for US$4.8 Billion.