Recent Yahoo news revealed that the company has faced a security breach with its email servers. Apparently, hackers were able to obtain hundreds of millions of accounts and are selling it in Russia's criminal underworld.

Hold Security founder Alex Holden has told Reuters that 272.3 million hacked user names and passwords for email accounts as well as other websites are being traded in Russia's underworld. The accounts were from Mail.ru, a Russian email service, Google, Microsoft and Yahoo.

It was noted that this has become one of the biggest number of stolen credentials to be uncovered over the past years. Holden and his firm have been successful in the discovery of some massive data breaches that affected Adobe, JP Morgan and Target.

The current security breach was found out after a young Russian hacker bragged about the stolen credentials in an online forum. It was said to total 1.17 billion records.

Holden added that the cache had about 57 million Mail.ru accounts, out of 64 million, after they eliminated the duplicates. It also contained millions of credentials from Google, Microsoft and Yahoo.

"This information is potent. It is floating around in the underground and this person has shown he's willing to give the data away to people who are nice to him," Holden, who is also the former chief security officer at U.S. brokerage R.W. Baird, said. "These credentials can be abused multiple times."

Mail.ru and Microsoft have confirmed with Reuters that they are already checking if any of the accounts are still active. Moreover, Microsoft has security measures set up for verification.

According to Ars Technica, Google and a Russia-based email service has questioned the validity of Hold Security's report. It seems that most of the rumored hacked accounts are fake.

"More than 98 percent of the Google account credentials in this research turned out to be bogus," a Google representative wrote in an e-mail to the publication. "As we always do in this type of situation, we increased the level of login protection for users that may have been affected."