Ireland's Data Protection Commissioner Helen Dixon has called on Yahoo to provide more clarity over the biggest hack in history.

The internet giant revealed yesterday that hackers stole data from around half a billion accounts in 2014, with Yahoo saying that the hack may have been state-sponsored.

As Yahoo’s European, Middle East and African operations are headquartered in Dublin, the office of data protection has responsibility for the regulation of the company in these territories. It is awaiting a response on the nature and extent of the security breach.

The data may have included names, email addresses and dates of birth, though Yahoo has moved to reassure people that it may not have gained unprotected passwords, payment card information or bank account details.

Yahoo had been advising its users to change their passwords over the past three days.

Online security expert Peter Turner said that it is important for organisations to respond in the right way, due to the "scale of the number of people who have been affected by it".

"It's becoming increasingly frequent," he noted, "the number of large companies who have had personal data taken from them."

It’s not clear how Yahoo's disclosure will affect the $4.8bn sale of the ailing giant's core internet interests (including Flickr and Tumblr) to the US communications group, Verizon.

The early online pioneer has been losing out to larger rivals such as Google and Facebook and has been consistently loss-making in recent years. 

Its share price remained steady at about $44 last night, however, indicating that investors think the Verizon deal will go ahead.