Per Yahoo’s release:
A recent investigation by Yahoo has confirmed that a copy of certain user account information was stolen from the company’s network in late 2014 by what it believes is a state-sponsored actor. The account information may have included names, email addresses, telephone numbers, dates of birth, hashed passwords (the vast majority with bcrypt) and, in some cases, encrypted or unencrypted security questions and answers. The ongoing investigation suggests that stolen information did not include unprotected passwords, payment card data, or bank account information; payment card data and bank account information are not stored in the system that the investigation has found to be affected. Based on the ongoing investigation, Yahoo believes that information associated with at least 500 million user accounts was stolen and the investigation has found no evidence that the state-sponsored actor is currently in Yahoo’s network. Yahoo is working closely with law enforcement on this matter.
Given that the unprecedented Yahoo data breach actually took place two years ago, questions remain as to why it has taken this long for the company to become aware of the hack.
The Yahoo data breach also has potential implications on the company’s upcoming sale to Verizon. AOL, another Verizon-owned company, issued a statement on the subject that, according to Re/code, appears to suggest that neither company was made aware of any issues on Yahoo’s side at the time the agreement was reached. What becomes of the Yahoo sales to Verizon after the dust clears on this remains to be seen.
In any case, Yahoo has begun notifying those account holders impacted by the hack. However, to be safe, if you have a Yahoo account, it might be best to just go ahead and change your password and security questions anyhow—along with the passwords of any other accounts that may be connected to or share a password with your legacy Yahoo password.