Over 270m email accounts have been hacked and sold to Russian underworld, a security expert has claimed.
While a majority of stolen usernames and passwords belonged to popular Russian email service Mail.ru, credentials for some of the world's biggest email providers were also compromised.
Of the 272.3m stolen accounts, nearly 40m addresses belonged to Yahoo, 33m were Microsoft and 24m were Gmail.
Alex Holden, founder and chief information security officer of Hold Security, told Reuters that the data breach is one of the world’s biggest cyber attacks.
The security chief discovered the data breach after his company came across blog posts by a Russian hacker claiming he has stolen over 1.17bn email records.
Holden told Reuters: "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. These credentials can be abused multiple times.”