"Today Equifax can confirm that a file containing 15.2m United Kingdom records dating from between 2011 and 2016 was attacked in this incident", the credit reporting agency revealed earlier today.
Equifax revealed on Tuesday that hackers accessed information on almost 700,000 British consumers in a breach earlier this year, significantly more than initially believed. The company, which holds data on around 820 million consumers and 91 million companies, said it faced a "massive" task responding to the hack.
Equifax first disclosed the breach on September 7, revealing that hackers exploited a vulnerability in a USA website application.
Equifax previously said that no password information or financial data was exposed - only names, dates of birth, email addresses, and telephone numbers.
The huge data breach was part of an attack on the firm's world-wide customer records in which the personal details of 146 million people in the USA were stolen, along with 8,000 Canadians.
Equifax has done it again.
The survey, sponsored by CyberScout, also found that more than 49 percent of respondents were confused about what to do after receiving a breach notification.
It said the initial estimate "was preliminary and did not materialise" and that the company planned to mail notifications to those affected with information about free credit monitoring and identity theft protection services.
Nearly 13,000 consumers had an email address associated with their Equifax.co.uk account accessed in 2014, while just under 15,000 consumers had portions of their Equifax membership details - such as username, password, secret questions and answers and partial credit card details - accessed.
Richard Smith, Equifax chief executive and chairman, stepped down in the weeks after the hack was reported.
"Equifax takes this illegal and unprecedented breach of consumers' data extremely seriously and has begun writing to the groups of consumers outlined below to notify them of the nature of the breach and offer them appropriate advice", the statement said.