We've recently discovered a vulnerability in our identicon generation process. To remedy it, we have changed how we approach generating them and regenerated all identicons. We do not have any indication that any personally identifiable information (PII) was leaked as part of this vulnerability.
Since 2013, we've been salting all identicon hashes, but still using email and IP addresses to generate them. Because of the sensitive nature of this type of data, we're moving entirely away from this method and instead will use an implementation going forward that does not involve any user-related information. Out of an abundance of caution, we're also forcibly changing all identicons across the Stack Exchange network, and chose to wait to communicate the change to you until the process was further along.
What are identicons?
Identicons are the default avatars we generate for users when they sign up.
I really liked my identicon, can I get it back?
While we do not recommend you to continue using your old identicon, we can give you back the image so that you may upload it as a custom avatar. Please contact us asking for it and we'll be able to give you the image.