Apparently, there was a serious data breach at LinkedIn and many customer records were stolen including “member email addresses, hashed passwords, and LinkedIn member IDs”. LinkedIn sent out a notification informing that the passwords were invalidated. What is interesting in the note is that they included a cryptic note that the break-in was “not new”. What could they mean by that?
On May 17, 2016, we became aware that data stolen from LinkedIn in 2012 was being made available online. This was not a new security breach or hack. We took immediate steps to invalidate the passwords of all LinkedIn accounts that we believed might be at risk. These were accounts created prior to the 2012 breach that had not reset their passwords since that breach.
I can take a wild guess that they passwords prior to 2012 were stored either unencrypted, without salt, or using some very weak algorithm. The security breach itself was, of course, “new” but the only information at risk are those passwords in the database that were stored in this old-fashioned way.
So, according to my wild guess, there must be more information stolen than they tell us but LinkedIn judged that the only information that threatens themselves were those old passwords so they finally invalidated them (what they should have done back in 2012) and told us they are happy with it.Unfortunately, there is no way to know for sure.
You can make your own wild guess at what happened.