The business social network is looking to quell user concern about the implications of their accounts being compromised by sending affected members emails with instructions on how to reset their passwords.
Those members will also receive a second email from LinkedIn’s customer support team with more context about the situation.
LinkedIn has also apologised for the situation on its blog and is tweeting updates and security tips from its @LinkedIn and @LinkedInNews Twitter accounts.
It is thought about 6.5 million accounts, a fraction of its total 161 million users, were compromised by hackers, who then posted a file containing encrypted passwords on a Russian internet forum.
IT security firm Sophos says the file does not contain associated email addresses but warned users that criminals would be working to try to assimilate the data. The company recommended users change their LinkedIn passwords immediately and should also use different passwords on other services.
The news comes in the same week LinkedIn admitted its mobile app had been sending data from users’ calendars – which could include meeting notes and phone numbers – without their consent. The company was forced to update the app to stop the data being shared.
Separately, dating site eHarmony has also confirmed a “small fraction” of its users’ data had been posted by the web. It did not provide further details about how many of its 20 million members might be affected.
EHarmony says on its blog that it has reset the passwords of affected users and will send them an email with instructions on how to set a new password.