The volunteer investigated further and found that when people ignored the warning, the attacker (1) stole the SSH password, (2) opened a connection to the server and observed all typed commands, and (3) opened a second connection and infected the server with Ebury.
To investigate the campaign, Kaba created a script that polled all of Tor’s roughly 3,000 exit nodes to check whether they received a correct SSH fingerprint from a test server. The test server then checked whether the connection came from a pinned exit node or one of 12 SSH interception servers used by the attacker. The volunteer further set up a honeypot to observe the interception software attempting to log in and install Ebury.
. . . The takeaway from the event is the crucial role in-depth defense plays in preventing data theft in mass hacks like this one. Those measures include configuring email accounts to accept only encrypted traffic and reject unencrypted ports. Another is to disable password authentication in favor of SSH keys.