UPDATE: Thank you for your patience — the issue has now been resolved. Your Desktop App should update the next time it launches — if it does not, please download it from webkinz.com again and re-install.
We are aware of the security message players are receiving when loading the Desktop App, however there has been no security breach and your accounts are safe.
Our technical team is currently working on a fix for the login issues. We appreciate your patience. The mobile app is not affected by this issue, so you can still log in to your accounts that way.