In reply to Konstantin Kovshenin.

It doesn't really sound like brute force, but rather a dictionary attack. It makes sense, really, especially in a time where everybody in the WordPress community are focused on the recent hacks/vulnerabilities.

If you want to see how long it would take to crack your password by brute force, see https://howsecureismypassword.net/ (if you trust the site not to save what you enter)
Note that Wordfence already has measures built-in their free version to limit login attempts.