Brute Force Attack

Brute force attack is a computer cracking technique in which the attacker uses anautomated program to try every possible combination for a password.This password attack does not attempt to decrypt any information but continue to try different passwords again and again to gain a authentication/access.The amount of time it takes to complete these attacks is dependent on length of the password.Traditional brute force attacks attempt to guess username and password combinations for services like FTP, SSH, or other authenticated 

Example

Let us assume the password length is 3. we have characters set (abcdefghijklmnopqrstuvwxyz0123456789)

Number of Permutation to first character :

Upper case letters(26 )+Lower Case Letters(26)+10 Numbers =62

Total permutation to find Password:

62*62*62=238328 ways. 

Thus the automated brute force program need to try for an 238028 possible password. You can also calculate the time take to complete the brute force attack from "Last Bit"

Tools for Brute Force Attack 

Here,I suggest some of the tools to crack an password using brute force technique

Cain and Abel

Aircrack

L0phtcrack

Brutus 

Advantage

Probability of finding the password high

Its fairly simple attack that doesn't require a lot of work to setup or initiate.

Disadvantage

Brute Force attack is noisy, and they take a long time

It takes an processing power and hardware intensive.

Nowadays a security measures is done that they might lock you out after 3 fail attempts and this extends the amount of time needed to crack