That means accounts created after 2015 are safe as their passwords weren't leaked?
I'm not sure but i can say all accounts which have been changed their passoword after that incident should be more safe.
This is really a surprising news I just found out that by the time of 2015 there was the incident that some accounts were hacked.
means this can be a lesson for us to be more careful and to be more secure we can try to change the password from now on to prevent the crime happen again
