What is brute force attack?
Brute force attack is a method to discover a password by systematically trying every possible combination of letters, symbols and numbers until it found the correct combination that works.
Brute force is not something that can be stop completely, but with some counter measures taken such as enabling captcha, brute force monitoring, fail2ban, allowing only trusted IP address for login page and etc, you can minimise the possibility of becoming brute force victim.
The best thing to do is to have strong password, long and unpredictable password, try to avoid dictionary words and change passwords regularly.
You can actually set Directadmin to blacklist IP address once it detected wrong password attempt in certain value. Refer below link for more information.
If you do not wish to receive notification from Directadmin regarding brute force attack, you can turn the notification off without disabling Directadmin protection at link below.