SAN FRANCISCO (NYTIMES) - Some time around August 2013, hackers penetrated the e-mail system of Yahoo, one of the world's largest and oldest providers of free e-mail services. The attackers quietly scooped up the records of more than one billion users, including names, birth dates, phone numbers and passwords that were encrypted with an easily broken form of security.
No one knows what happened to the data during the next three years. But last August, a geographically dispersed hacking collective based in Eastern Europe quietly began offering the whole database for sale, according to Mr Andrew Komarov, chief intelligence officer at InfoArmor, an Arizona cybersecurity firm.
Three buyers paid about US$300,000 (S$432,929) each for a complete copy of the database, he said.
Yahoo said on Thursday (Dec 15) it could not verify Mr Komarov's claims, which were made public in a Bloomberg article on Wednesday.
The attack, which Yahoo disclosed on Wednesday, is the largest known data breach of a company. And neither Yahoo nor the public had any idea it had occurred until a month ago, when law enforcement authorities came to the company with samples of the hacked data from an undisclosed source.
Yahoo still does not know who broke into its systems in 2013, how they got in or what they did with the data, the company said.
It has made more progress tracking down a separate hacking episode in 2014, which compromised 500 million e-mail accounts and was disclosed in September. The company has said it believes the 2014 attack was sponsored by a government entity but has not identified it.
The two huge breaches revealed this fall threaten to erode consumer confidence in the company and are endangering its deal to sell its internet businesses to Verizon Communications for US$4.8 billion.
On Thursday, Yahoo's stock plunged 6 per cent as investors worried that Verizon would abandon the purchase.
The FBI said in a statement that it was investigating the Yahoo breach. New York attorney-general Eric Schneiderman also said his office was in touch with Yahoo to examine the circumstances of the data breach.