In June the web firm announced Yahoo addresses and IDs would be reassigned if they had been inactive for a year.
Privacy experts called on Yahoo to address the issue "immediately". Yahoo says it has taken a series of measures to overcome privacy and security fears.
"Before recycling inactive accounts we attempted to reach the account owners [in] multiple ways to notify them that they needed to log in to their account or it would be subject to recycling," a Yahoo representative told.
