Price comparison site Compare The Market is reviewing security after a newspaper investigation exposed failings in its current system.
The Sunday People revealed that only an email, surname and date of birth were required to access a Compare The Market account.
The lack of a password-protected system meant personal data – including address, value of home contents and marital status – were all at risk of being hacked by fraudsters and could have left users at risk of being burgled, or having their information used to apply for financial products such as credit cards.
Compare The Market has now stopped site users from accessing the data.
Customers attempting to log into the site now receive the following message: "We are upgrading our website with a new password system. Please come back tomorrow to retrieve your old quotes or simply start a new comparison using the icons below."
The Information Commissioner's Office is currently investigating the security breach.
A Compare The Market spokesperson says: "We take the safety of our customers' data very seriously and have moved immediately to put in place a new password protection system and remove this issue.
"We'd like to reassure our customers that this issue has been rectified but, should they have any questions, invite them to contact us directly."
Compare The Market user? Protect your data
Set a password as soon as possible. Compare The Market’s new password system is expected to be up and running by tomorrow. Log in as soon as you can and set a password to protect your information.
If you have any other concerns, Compare The Market can be reached by email at: firstname.lastname@example.org.