Any time I think about Sony and irregular activity, I think of the huge PSN blackout that happened a while ago. While nothing seems to be as problematic as that, Sony may be forcing some US PSN users to reset their passwords. A post on the PlayStation forums advises users experiencing sign-in issues to reset and change their passwords as a precaution.
A moderator stated, “If you are getting an error that your PSN account password is incorrect, you may need to reset it. We routinely monitor for irregular activity, and if such activity is detected, we may sometimes reset passwords of affected SEN accounts to protect consumers and their account information.”