Yahoo said Wednesday that more than 1 billion user accounts – meaning most of the Internet giant’s customers worldwide – were hacked in 2013, leading to the release of user names, telephone numbers, dates of birth and other personal information.
News of the hack, coming after the announcement in September of a separate hack affecting 500 million accounts, means that Yahoo has been the victim of the two largest data breaches ever reported. Both have been announced since Yahoo agreed to sell its core businesses to telecommunications giant Verizon in July for $4.8 billion.
The incident raised new questions among analysts regarding the viability of that deal and whether the valuation will need to be changed, especially if the hacks trigger litigation against the company.
“This is another major blow,” said Jeff Kagan, a Georgia-based telecommunications industry analyst. “It throws into question what’s really going on at Yahoo. And if you don’t really know what’s going on at Yahoo, does Verizon have the guts to buy a potential bomb? This company could explode with major problems and major losses.”
In the 2013 incident, Yahoo said that credit card and bank account numbers, which are stored separately, were not affected, but the breach did include some unencrypted “security questions” that the company uses to authenticate users.
Yahoo also reported a separate incident Wednesday in which hackers used what the company called “forged cookies” to gain access to some accounts, though it did not give the number. That incident, the company said, appeared to have links to the one announced in September involving “state-sponsored” attackers. Law enforcement officials said that breach, which happened in 2014, was probably the work of Russian hackers, though no final conclusion has been reached.