The hack in which scores of passwords were stolen from Linkedin and eHarmony may have first occured last year.
Users on the forum insidepro – to which the encrypted stolen passwords were posted – told CRN sister site SC Magazine they found their old LinkedIn passwords in the encrypted cache that were obsolete for between six and nine months.
Those users had regularly updated their passwords, placing the hack in about a three month period from around January.
Others claimed inside knowledge that the hack occured around the start of the year through SQL injection on the LinkedIn web site.
LinkedIn refused to verify or refute the claims.
“Due to the ongoing investigation, we aren't disclosing the specific details and data related to what we found,” communications manager Deepa Sapatnekar said in a statement.
“The point is we were quickly able to confirm that these were in fact stolen LinkedIn passwords.”
The orginal uploader of the affected password cache, dwdm, did not respond to requests for comment.
Compromised passwords that appeared in the swiped cache were not tied to LinkedIn accounts - meaning each combination may have been used by multiple users.
LinkedIn has now reset all affected passwords.
About 5.8 million passwords from LinkedIn and eHarmony were posted to insidepro on 3 June. The credentials were stolen before Linkedin had a chance to implement stronger security measures, including salting.