wp-admin on login shows username

when I bring up http://jfktest.jfkwebdesign.com/wp-admin/ (or any one of my other WordPress sites.), the username is already displayed.
I would think this is a security issue.
I know that in the past, I have typed a single character and several possible usernames have been displayed.
Is there a fix that forces this field to be blank without offering any possible entries?
Thank you.
As a long time “scratch” PHP, MySQL programmer, I am loving WordPress!!
John