Millions of emails and passwords have been compromised and posted to a hacking forum in a major data breach.

According to security researcher Troy Hunt, more than 700 million emails and 20 million passwords were exposed. Hunt runs the website, haveibeenpwned.com, a site that helps users find out if their information has been compromised.

Hunt told Wired.com that it is difficult to see where the information originated from, but that it could have come from more than 2,000 leaked databases. Wired reports that this type of breach has happened before, but never at this scale.

Cybersecurity expert Scott Schober says that hackers can use this information in a variety of ways.

“They can perform identify theft or to try to take credit in our name,” he says.

Schober is the president and CEO of Berkeley Varitronics. He says that while cybersecurity threats can’t be 100 percent prevented, there are some ways users can protect themselves.

“Considering using a password manager,” he says. “Having a few email accounts. It’s more to manage but it allows you to keep the secure stuff secure.”

Schober also recommends using websites that officer two-factor authentication for added protection.