Hacking Attempt EVERY 4 minutes! Like clockwork! What can I do?

Hi,
I have better wp security (thank god) and its preventing a hacking attempt for the last 2 hours!

Here’s the scene:
1) Somehow, the hacker has found out my username (its not admin or the usual ones), I REALLY don’t know how they got it and from where.

2) Now, every 4 minutes, they are trying to attack with a brute force login attempt, but of course better wp security is blocking them out for ‘too many attempts’.

3) But Worse – They are trying each new attempt from a different ip so that better wp security can’t stop the new ip.

So what now?? How long will this go on? What can I do proactively?