Brian Krebs @ his "Krebs on Security" blog:
Just months after disclosing a breach that compromised the passwords for a half billion of its users, Yahoo now says a separate incident has jeopardized data from at least a billion more user accounts. The company also warned attackers have figured out a way to log into targeted Yahoo accounts without even supplying the victim’s password.
On September 22, Yahoo warned that a security breach of its networks affected more than 500 million account holders. Today, the company said it uncovered a separate incident in which thieves stole data on more than a billion user accounts, and that the newly disclosed breach is separate from the incident disclosed in September.
My Yahoo Account Was Hacked! Now What?