Ophcrack is a free open-source (GPL licensed) program that cracks Windows log-in passwords by using LM hashes through rainbow tables.

The program includes the ability to import the hashes from a variety of formats, including dumping directly from the SAM files of Windows, and can be run via the command line or using the program’s GUI (Graphical user interface).

[1] Rainbow tables for LM hashes are provided for free by the developers.

[3] Larger rainbow tables are NTLM hash for cracking Windows Vista/Windows 7.

[4] Ophcrack is also available as Live CD distributions, which automates the retrieval, decryption, and cracking of passwords from a Windows system.