Affected users may be asked additional security questions when logging in as Yahoo adds extra security to accounts
Yahoo has improved its security systems after 450,000 email addresses and passwords were posted online.
The company said that it had fixed a vulnerability that allowed hackers to access a database containing user information dating back to 2010. In July a hacking group called D33DS said it had carried out the attack as "a wake-up call and not a threat".
Yahoo said the data was from people who had joined the Yahoo Voice service prior to May 2010, when it was owed by another company and called Associated Content. In a statement Yahoo said it had enhanced "underlying security controls" and was also in process of notifying affected users.
People may be asked additional security questions when they next login to their Yahoo account to confirm they are the account holder.
Updating your subscription status