I'm not sure that I necessarily agree with your estimate of 20,000+ attempts to guess someone's password, it depends how stringent your password policy is. If it's fairly lax and you're allowing simple dictionary words (i.e. no requirement for numbers, capital letters or punctuation), not only are you allowing passwords that are easier to brute force, but you're also allowing your users to choose words which may be very commonly used passwords because they're easy to remember. I'd be willing to bet that there are about 10 strings which are used as passwords far more often than other strings. Things like 'password', 'changeme' and 'abc123' would be at the top of my list of passwords to try even before beginning a brute force attack because chances are if you don't have a strict password policy I can break into someone's account this way with very little effort.

Also make sure that you give the same message when someone tries to log in as a user who doesn't exist as when a user who does exist logs in with the wrong password. Something along the lines of "Your username and password do not match" rather than "That user doesn't exist" and "Your password is incorrect". That way if someone is trying to get in who shouldn't and they don't know any of your user's login names it's not so easy for them to find out what they are. Using graff's analogy, don't make it any easier for them to find the door if they don't know where it is.

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"Write a wise saying and your name will live forever." - Anonymous

In reply to Re: Why do you have to worry about Brute Force Attacks? by Nevtlathiel
in thread Why do you have to worry about Brute Force Attacks? by Anonymous Monk

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