HOW HACK-FRIENDLY IS YOUR PASSWORD? INFOGRAPHIC
The ability to crack passwords using computer programs is also a function of the number of possible passwords per second which can be checked. If a hash of the target password is available to the attacker, this number can be in the billions or trillions per second, since an offline attack is possible.
So, to break an 8 character password, it will take (1.7*10^-6 * 52^8) seconds / 2, or1.44 years. Note that on a GPU, this would only take about 5 days. On a supercomputer or botnet, this would take 7.6 minutes. As you can see, simply using lowercase and uppercase characters is not enough.