Whenever anyone thinks How to hack or crack the Passwords then JTR is the first software that comes in the mind of every hacker. Its the Best Password Cracking tool available. The main thing that makes it more popular is that its an open source freeware.
John the Ripper is a fast password cracker, currently available for many flavors of Unix, Windows, DOS, BeOS, and OpenVMS. Its primary purpose is to detect weak Unix passwords. Besides several crypt(3) password hash types most commonly found on various Unix systems, supported out of the box are Windows LM hashes, plus many more with contributed patches.
Note: a few Windows "antivirus" and "anti-spyware" products have started to recognize password recovery tools as if they were "trojans". This is how those products' vendors inflate their detected "virus" counts. The effect is that end-users are no longer able to check password recovery software forreal viruses. If this affects you, please complain to your antivirus vendor.