Handling Invalid Usernames

Could someone please take a look at the pseudo-code below and let me know your thoughts on how I am handling Invalid Usernames?

Invalid Username
At {Authenticate Customer}, if the System cannot find the Username…
The System logs the User’s IP Address. ???
The System informs the User that the Log-In failed.
The System asks the User to try again.
The use-case continues at {Authenticate Customer}.
{Match Found}
If the User enters a valid Username, the use-case resumes at the next step…
{No Match Found}
If the User does not enter a valid Username after 3 attempts…
The System logs the failed attempt.
The System notifies the System Administrator.
The System blocks the IP Address in question. ???
The use-case ends.