Yahoo says one billion of its accounts were breached back in August 2013.

It now stands as the largest hack of consumer data in history.

If you've ever had an account, even one you haven't used for 10 or 15 years, your information may have been at risk for more than three years.

Yahoo apparently didn't know about the hack until federal investigators got their hands on the stolen info from hackers on the dark web, according to cyber security expert and certified ethical hacker Charles Tendell.

Tendell says there are plenty of other accounts, besides your Yahoo account you need to be concerned about.

"Was that username (or password) used for anything else? Can that account now be used to create spam to people you might have interacted with? What about the people who are in your contact list that may still use their yahoo account?" Tendell said.

Yahoo did say that no credit card information was included in the information that's been hacked.

Tendell says any bank accounts that may have been linked to your Yahoo account or email may be at risk, however.

He says step one to protecting yourself is always changing your password.

There are tools online that Tendell recommends to help track down any extra accounts that may be at risk.

haveibeenpwned.com and pipl.com allow you to enter emails or usernames to see if there are any breaches that may affect those accounts.

Tendell is host of the podcast The Charles Tendell Show.