Qualys researcher Francois Pesce used open source password cracker John the Ripper to try to crack SHA-1 hashes of leaked LinkedIn passwords. He ran the John the Ripper default command on a small default password dictionary of less than 4,000 words. The program then switched to incremental mode based on statistical analysis of known password structures, which generated more probable passwords.
The results? After 4 hours, approximately 900,000 passwords had been cracked. Francois then ran numerous iterations, incorporating older dictionaries to uncover less common passwords and ended up cracking a total of 2,000,000 passwords.