Hiding wordpress dashboard login error is very basic thing for keep away hackers. Whenever you and any hackcer are trying to login using the correct username but with the wrong password, that will give you a message saying “Error: Incorrect Password.” hacker will got the clue that the username entered is in the system, and that they simply need to crack its password. Same with username also you will got following message.
“Error: Invalid username”
For avoiding this thing you just need to open your functions.php file and put the following code in that file
add_filter('login_errors', create_function('$a', "return null;"));
This hack will remove the WordPress error by displaying nothing when a login is incorrect.