Obviously you shouldn’t use this to gain unlawful access to a computer. If you’re a geek, however, you’ll eventually end up in a situation where someone forgets their password, you acquire a machine with an operating system you cannot access, or similar situation.

Windows

Ophcrack

Windows is still the most popular operating system, and the method used to discover the login password is the easiest. The program used is called Ophcrack, and it is free. Ophcrack is based on Slackware, and uses rainbow tables to solve passwords up to 14 characters in length. The time required to solve a password? Generally 10 seconds. The expertise needed? None.

Simply download the Ophcrack ISO and burn it to a CD (or load it onto a USB drive via UNetbootin). Insert the CD into a machine you would like to gain access to, then press and hold the power button until the computer shuts down. Turn the computer back on and enter BIOS at startup. Change the boot sequence to CD before HDD, then save and exit.

Ophcrack cracks Windows password based on rainbow tables. It is a very efficient implementation of rainbow tables done by the inventors of the method.

Cain & Abel

Cain & Abel is a password recovery tool for Microsoft Operating Systems. It allows easy recovery of various kind of passwords by sniffing the network, cracking encrypted passwords using Dictionary, Brute-Force and Cryptanalysis attacks, recording VoIP conversations, decoding scrambled passwords, recovering wireless network keys, revealing password boxes, uncovering cached passwords and analyzing routing protocols. The program does not exploit any software vulnerabilities or bugs that could not be fixed with little effort. It covers some security aspects/weakness present in protocol’s standards, authentication methods and caching mechanisms; its main purpose is the simplified recovery of passwords and credentials from various sources, however it also ships some “non standard” utilities for Microsoft Windows users.

[Download Cain & Abel v4.9.35 for Windows NT/2000/XP
MD5 - B834105299960CC2B86CE33CCE8C14CE
SHA1 - E7F2954571EF1B75328CD2F055042B3F5C6F2B14]

Mac

The second most popular operating system, OS X is no safer when it comes to password cracking then Windows.

The easiest method would be to use Ophcrack on this, also, as it works with Mac and Linux in addition to Windows. However, there are other methods that can be used, as demonstrated below.

If the Mac runs OS X 10.4, then you only need the installation CD. Insert it into the computer, reboot. When it starts up, select UTILITIES > RESET PASSWORD. Choose a new password and then use that to log in.

If the Mac runs OS X 10.5, restart the computer and press COMMAND + S. When at the prompt, type:

fsck -fy

mount -uw /

launchctl load /System/Library/LaunchDaemons/com.apple.DirectoryServices.plist

dscl . -passwd /Users/UserName newpassword

That’s it. Now that the password is reset, you can login.

Linux

Finally, there is Linux, an operating system quickly gaining popularity in mainstream, but not so common you’re likely to come across it. Though Mac and Linux are both based on Unix, it is easier to change the password in Linux than it is OS X.

To change the password, turn on the computer and press the ESC key when GRUB appears. Scroll down and highlight ‘Recovery Mode’ and press the ‘B’ key; this will cause you to enter ‘Single User Mode’.

You’re now at the prompt, and logged in as ‘root’ by default. Type ‘passwd’ and then choose a new password. This will change the root password to whatever you enter. If you’re interested in only gaining access to a single account on the system, however, then type ‘passwd username’ replacing ‘username’ with the login name for the account you would like to alter the password for.

Conclusion

There you have it – that is how simple it is for someone to hack your password. It requires no technical skills, no laborious tasks, only simple words or programs. The moral of the story? Encrypt your data to keep it safe. Don’t use only a password, but actually encryption, such as Blowfish or AES-128. There are a number of programs that can do this – TrueCrypt for Windows, or the native encryption found on Ubuntu, creating a disk image in Mac, etc.

Reference:

http://www.joetech.com/2009/01/29/how-to-crack-the-account-password-on-any-operating-system/