A common method of gaining access over a server is to use a technique called a brute force attack, or dictionary attack. What the attacker will do, is use a script to try and login to an account with every possible password combination. This tends to require tens of thousands of login attempts, but eventually, the right combination will be found, and they can login normally.
To prevent this, we can use brute force login detection system.
Step 1 : Login to DirectAdmin as admin.
Step 2 : Select Administrator Settings under Extra Features.
Step 3 : Tick on Blacklist IPs for excessive DA login attempts and you can use 10-20 value for login attempts.
Step 4 : Make sure to tick on Prevent 127.0.0.1 from being Blacklisted. Select on Save.