Cybersecurity professionals are warning anyone with a personal email account to change their passwords after stolen user names and passwords were being offered up for sale on the Internet, NBC News reported.
Some 272.3 million accounts were stolen - and involve some of the biggest email providers, including Google, Yahoo, Hotmail and Microsoft, according to Alex Holden of Hold Security.
"We know he's a young man in central Russia who collected this information from multiple sources," Holden told NBC News. "We don't know the way he did it or the reason why he did it."
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The user names and passwords were all being sold on the so-called “dark web,” where hackers hock their goods. Hackers use the stolen information to lure users into giving away more information, including credit card numbers and bank account access.
Experts say people should change their passwords regularly. Use abstract combinations of letters, numbers and characters that a criminal's computer program couldn't easily guess.