As computing power increases, passwords become more vulnerable. Once upon a time, an eight-character password was thought to be strong protection, but a password cracking company has constructed a computer that uses the GPUs of 25 AMD Radeon video cards to mount a massive brute force attack by guessing 350 billion possible passwords per second. This means it can try every single possible eight character password (that includes alphabetic, numeric and symbol characters) in five and a half hours.
This highlights the necessity to protect against brute force attempts with technologies such as account lockout after a set number of failed attempts.
You can read more about the password-cracking computer here: