Deputy Information Commissioner Simon Entwisle said:
“This latest report of another significant data loss at Yahoo gives us further cause for concern.
“We’d expect any formal investigation to be handled by US and European authorities, but the ICO will continue to make its voice heard on behalf of people affected in the UK.
“We are talking to Yahoo again today and we are in touch with the relevant international authorities to ensure the data protection interests of UK customers are considered.
“The scale of this attack is unprecedented and it is not yet known how many UK users are affected. We would urge all Yahoo users who have not changed their passwords recently to consider doing so now.”