Apparently, they are a hacker group who posted messages today about the change that took place on Tibia and made the login system possible only with the password and e-mail. They claim that this made possible the hack of a big number of old accounts.
As far as I could track, people mentioned this group on the official Tibia board discussing this change and also on Reddit I could see this post signed by one of the members of this group:
Official board discussion: https://www.tibia.com/forum/?action=thread&threadid=4731861&pagenumber=1
Reddit message signed by a HongKong.exe member: https://www.reddit.com/r/TibiaMMO/comments/c8aa4b/shout_out/
I can't confirm if mass hacks are happening, but since there are many old/abandoned Tibia websites around, we can assume that there is a big chance that these websites had a very weak encryption of personal data, which made them exposed to hacker attacks. With this and added to the fact that many people tend to use the same password on every service, specially when we think about old forums a decade old, they can at least guess your email account if they look at users that they can correlate with existing Tibia characters. If you still use a really old password that was the same that you used to access Tibia fansites since a long time, you really need to change your password as soon as possible.
In my opinion, it is a good time to start using the official Tibia authenticator.