Dear Sir or Madam

We are contacting you today to inform you of a potential security risk
in the SSH service of the following rented servers:

...

An SSH server uses host keys to uniquely identify itself to connecting
clients. These keys are normally automatically regenerated each time a
new installation of the operating system is done.

Due to an error in the installation software introduced on April 10th,
2015, the Ed25519 SSH host keys (/etc/ssh/ssh_host_ed25519_key) on our
standard images were no longer individually regenerated.

This resulted in identical Ed25519 SSH host keys for each affected OS
image.

ле хецнер