Russian crime gangs own 1.2 billion passwords and usernames and 500 million email addresses stolen in brazen hacking attacks since last year.

An Internet security company based in Milwaukee said the passwords and email addresses were stolen during cyber attacks that struck 420,000 websites.

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The haul is believed to be the single biggest cache of stolen Internet credentials ever gathered to date, said Hold Security, an Internet security firm.

Hold Security has a record of tracking huge Internet breaches, such as the theft of tens of millions of data from Adobe Systems in 2013.

"Before, we were amazed when 10,000 passwords [went] missing. Now we're in the age of mass production of stolen information," Alex Holden, the company's founder and chief information security officer, told IDG News Service.

The Internet security firm didn't name the sites that were compromised, citing nondisclosure agreements and to protect sites that are still vulnerable.

It said the list included small websites and prominent names on the Internet.

A computer crime expert recruited by The New York Times confirmed the stolen information is genuine. Another independent security authority said a few big firms were aware that its documents were included in the stolen data.

The massive size of the stolen data overshadows similar thefts in the past. Hackers from Russia and Eastern Europe recently stole 70 million private records and 40 million debit and credit card details from American retail giant, Target Corporation.

The string of attacks was one of the biggest security breaches in history. Security experts said the brazen actions of  Russian cybercriminals take identity theft to a new degree.

"These guys did nothing new or innovative," said Holden. "They just did it better and on a mass level so it affects absolutely everybody." 

Tagshackers, Russian, Russian crime, cybercrime, cyber spying, cybersecurity, credentials, Credit Card, passwords, Adobe Systems