Sometimes the following message shows up in the Server's Log file, especially if the server is on a common port like 21 or 80.
Error Message: 9/31/2015 19:02:12 : 0 : 8.4.10 : WARNING: Possible Hack Attempt. Cramming multiple password attempts FORCED CLOSE REQUESTED
There are some creeps on the internet who use automated scripts to seek out servers to exploit.
Your RBS Server has built-in security countermeasures that detect and block hackers.
Attempted intrusions happen mostly on port 21. No port is perfectly safe from attempts to connect, but 21 is the known and expected port used by many FTP servers, so it is a favorite target of hackers.
If you put your RBS server on port 21 you will likely see this message in your logs. It means your RBS Server is safe.