Experian says personal information from up to 143 million U.S. consumers has been compromised.
RELATED: 7 on Your Side: Is identity theft insurance worth it?
This is not just any security breach; Equifax is one of three leading credit bureaus in the country.
The breach involves names, social security numbers, date of birth and addresses.
Compare that to the Target breach of 2013 when there were 41 million victims.
So what happened? Equifax says the hackers exploited the websites vulnerability.
ABC News is reporting the FBI is already investigating the case.
The company discovered this breach on July 29. There's no explanation of why it waited so long to report it.
What should you do as a consumer? Go to the Equifax website, click on "potential impact" and Equifax says it will tell you if you were affected by the breach.
RELATED: Hijack hacks: What you need to know about 'ransomware'
You will need to put in your last name and six digits of your social security number
You will receive a date when you can enroll in the Equifax credit monitoring service "free for one year," even if you were "not affected" by the breach.
Click here for more details on the hack and to find out if your info was impacted.