Question about login attempts

One of my WordPress installations is under attack and has been for a while now. Today, I’ve noticed login attempts using a number as the login id instead of an alphanumeric string of characters, like a username like “bob” or “admin”.

I’ve got some security measures in place and I’m actively monitoring things but I wanted to see if anyone knew of any past WordPress exploits involving logins or login attempts using a number, like 0, 1 50, 100, etc., instead of an expected alphanumeric string, like “bob7” or “admin”?

Thanks!

Peace…