Yahoo reveals further data breach from 2013, over one billion affected

US internet firm Yahoo has revealed another massive data breach from 2013 which affected more than one billion of its users.

Earlier this year, the company admitted a separate hack of 500m accounts dating back to 2014, which it stated was a "state-sponsored" attack. Names, phone numbers, passwords and email addresses were stolen.

Yahoo is currently in the midst of being taken over by telecommunications giant Verizon in a deal worth at least $4.8bn, but the latter was reported to be considering negotiating a lower amount after the damage caused due to the initial hack.

In a statement released by Yahoo, it said that it does not believe the two incidents are connected.

"Based on further analysis of this data by the forensic experts, Yahoo believes an unauthorized third party, in August 2013, stole data associated with more than one billion user accounts," the statement said.

It also added that its security experts have been unable to identify the source of the breach.

"The company has not been able to identify the intrusion associated with this theft. Yahoo believes this incident is likely distinct from the incident the company disclosed on September 22, 2016."

Cyber-security has become a hot topic for businesses and lawmakers alike as the amount and severity of such attacks increases year-on-year. On Wednesday Donald Trump met with US tech CEOs to discuss a variety of issues, with cyber-security thought to be high up the agenda.

One security expert said that Yahoo had a responsibility to its customers to ensure no more data is breached.

“Yahoo should know that it is an invaluable target for cybercrime syndicates and nation-states and invest the resources to protect its data accordingly," said senior research scientist at Comodo, Kenneth Geers. "The use of vulnerable MD5 hashes suggests that Yahoo was not paying sufficient attention to security."