A “brute-force” attack is a type of cyber attack that relies on a system of trial and error– trying every possible combination of characters to crack an encrypted piece of information, such as a password. Imagine someone trying to crack the combination for a lock by trying every possible combination of numbers: this would be classified as a brute force attack. Although brute-force attacks eventually work, they can understandably be quite time consuming. Hackers usually use an automated system that guesses possible passwords at a much faster rate than any person could. Generally, the longer the password, the longer it takes for a computer to crack it.
A hacker can have many different motivations behind committing a brute-force password cracking attack. Hackers often want to steal important information, use certain information to blackmail their victim, delete or alter information, or preform espionage on their victim.
Source: Brute force attack