The cyberattack, which took place in May but only came to light in September, exposed 143 million people to the risk of identity theft, mostly in the US.
Equifax company has now revealed it believes 693,665 UK customers are at risk following the attack.
Hackers could have accessed personal details including home addresses, email addresses, driving licence numbers or partial credit card information.
Equifax is a consumer credit reporting agency with data on more than 800 million individuals and 80 million businesses worldwide.
The company is set to write to customers believed to be at risk and offer them free account monitoring services.
In a statement announcing the risk to UK consumers, Equifax’s Europe President Patricion Remon said: “I would like to extend my most sincere apologies to anyone who has been concerned about or impacted by this criminal act.
“Let me take this opportunity to emphasise that protecting the data of our consumers and clients is always our top priority.”