Yahoo has confirmed that the company was the victim of a hack in 2014 in which data on 500 million users was stolen.
Reports of the losses first surfaced in August this year, but the firm did not confirm or deny anything at the time
However, after an investigation into the situation, Yahoo chief information security officer Bob Lord has now confirmed that the hack did indeed take place and that state-sponsored attackers were probably responsible.
"A recent investigation by Yahoo has confirmed that a copy of certain user account information was stolen from the company's network in late 2014 by what it believes is a state-sponsored actor," he said.
"The account information may have included names, email addresses, telephone numbers, dates of birth, hashed passwords (the vast majority with bcrypt) and, in some cases, encrypted or unencrypted security questions and answers."
There is some good news relating to personal information, which is mostly secure. Still, this is only a slight positive when you consider what actually went on.
"The ongoing investigation suggests that stolen information did not include unprotected passwords, payment card data or bank account information. Payment card data and bank account information are not stored in the system that the investigation has found to be affected," added Lord.
"Based on the ongoing investigation, Yahoo believes that information associated with at least 500 million user accounts was stolen, and the investigation has found no evidence that the state-sponsored actor is currently in Yahoo's network. Yahoo is working closely with law enforcement on this matter."
Yahoo has claimed that the attackers are no longer in its systems, but Kevin Bocek, chief security strategist at Venafi, is dubious that the firm can be so confident.
“It’s almost certain that the attackers have used Yahoo’s own encryption against it. There is no way that this much data could be stolen without encryption being used to get the data out of the Yahoo network; if it hadn’t been, alarm bells would have rung loud and clear," he said.
"In 2014, Yahoo began turning on encryption by default for all web traffic with HTTPS. Worryingly, this is probably why Yahoo won’t know whether the attackers are still active or in its systems as they could be using encryption to hide and look trusted. Yahoo, like most organisations, is unable to look inside its own encrypted traffic."
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