Personal information involving millions of people – including Social Security numbers – has reportedly been stolen in a massive hack of a background check company.

According to a proposed class action lawsuit, National Public Data, owned by Jerico Pictures Inc., failed to properly safeguard information it scraped from other sites, USA Today reported. The information reportedly includes as many as 2.9 billion full names, current and past addresses, Social Security numbers and information on parents, siblings and other relatives.

The data breach, which occurred in April, was reportedly the work of a hacker group called USDoD which accessed the unencrypted personal information. Earlier this month, a hacker leaked some of the stolen data for free on a hacking forum, according to tech site Bleeping Computer.

“Each record consists of the following information – a person’s name, mailing addresses, and social security number, with some records including additional information, like other names associated with the person. None of this data is encrypted,” Bleeping Computer reported after a review of the leaked data.

What should you do?

Experts recommend freezing your credit files at the three major credit bureaus – Experian, Equifax and TransUnion. This will prevent someone from using your information to apply for a loan but you will have to lift the freeze if you apply for a loan oe credit card, or open a new account.

You can go here to see more information on freezing your credit report.

You should also be vigilant about clicking links on unsolicited emails or text messages and monitor your credit report.