SSH, as implemented in OpenSSH before 4.0 and possibly other implementations, stores hostnames, IP addresses, and keys in plaintext in the known_hosts file…

SSH, as implemented in OpenSSH before 4.0 and possibly other implementations, stores hostnames, IP addresses, and keys in plaintext in the known_hosts file, which makes it easier for an attacker that has compromised an SSH user's account to generate a list of additional targets that are more likely to have the same password or key.