Amazingly enough, this is another topic that engenders a bit of controversy. I mean, nobody denies the wisdom of automatically locking out user accounts that are under attack. The controversial part concerns the number of failed login attempts that we should allow before locking the account.
Back in the stone age of computing, so long ago that I still had a full head of hair, the early Unix operating systems only allowed users to create a password with a maximum of eight lowercase letters. So in those days, it was possible for early man to brute-force someone else's password just by sitting down at the keyboard and typing in random passwords. That's when the philosophy started of having user accounts get locked out after only three failed login attempts. Nowadays, with strong passwords, or better yet, a strong passphrase, setting...