Protected wp-login is a WordPress plugin by alvego for protecting your login form.
Plugin implements setting the security key for the login form, thereby significantly reducing the likelihood of automatic brute force. The security key is transmitted manually as GET parameter for login form.
For example: http://example.com/wp-login.php/wp-login.php?sk=my_secure_key
If sk parameter is not specified, the login will not be possible, even if specifying the correct username and password. When logging in, without specifying the correct security key, the current php process freezes for a few seconds, which also complicates the brute-force and reduces the load on your server in case of attack.