Owners of redesignated email addresses are getting personal emails intended for the former owner.
Yahoo's ploy in June to reassign addresses which had been inactive for a year or more has been criticised after new owners have been able to collect personal details on the former user of the address.
New owners have written to tech blogs to say they can access previous owners' social networking accounts, addresses, phone numbers, and even social security numbers.
Yahoo has said it took a number of precautions, including leaving the accounts dormant for 30 days, during which time it notified correspondents that the account had been deactivated.
It has announced it is now addressing the issue.
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