How long?
Depends.
For weak passwords, minutes.
For strong passwords, thousands of years.
http://www.gizmodo.com.au/2011/02/how-long-it-takes-hackers-to-crack-your-password/ / security verify verification alphabetic numeric punctuation spaces eight characters remember random mix mixture upper lower case number numbers numerals punctuation symbols dictionary word English foreign alphabet secret reveal Fast Identity Online Alliance FIDO /
