Yahoo! is facing a lot of challenges lately. Add to the heap the breach – which the company confirmed today – that has affected 500 million Yahoo! accounts and is believed to have been carried out by a state-sponsored actor.

The breach, which dates back to late 2014, may have allowed unauthorized parties to access such information as Yahoo! account holder dates of birth, email addresses, names, telephone numbers, and security questions and answers (both encrypted and unencrypted), the company said. Yahoo! doesn’t think the breach included the theft of bank account information, payment card data, or unprotected passwords.

The company sent out an email and posted on its website a letter from Yahoo! CISO Bob Lord explaining the situation and what it is doing to protect its users. Yahoo! in the communications said it has invalidated unencrypted security questions and answers so they can’t be used to access an account, is working closely with law enforcement on the matter, and continues to upgrade its systems to identify and prevent unauthorized access to user accounts.

The company is also suggesting affected users change their passwords and adopt an alternate means of account verification, review their accounts for suspicious activity, avoid clicking on links or downloading attachments from suspicious emails, use caution in responding to unsolicited emails, and consider using the authentication tool Yahoo Account Key. Users with Yahoo Account Key don’t need passwords to sign into their accounts.

“Since we don’t have the specifics yet, it will be hard to say how everything happened,” notes Brad Bussie, CISSP, director of product management at STEALTHbits Technologies. “What we do know is that accounts that have been breached have value. The reason they have value is that people use the same password for multiple sites. The industry has been warning users for years that they need different complex passwords for each account they use online. The problem is that many consumers have dozens of accounts and remembering that many passwords is hard.”