Alpha-numeric passwords were first introduced in the 1960s as a solution to security issues that became evident as the first multi-user operating systems were being developed. As the name indicates, an alpha-numeric password is simply a string of letters and digits. Although almost any string can serve as a password, these passwords only offer good security as long as they are complicated enough so that they cannot be deduced or guessed.

Commonly used guidelines for alpha-numeric passwords are:
The password should be at least 8 characters long.
The password should not be easy to relate to the user (e.g., last name, birth date).
The password should not be a word that can be found in a dictionary or public directory.
Ideally, the user should combine upper and lower case letters and digits.

Since the best password would be a completely random one, people have devised ways to create pseudo-random passwords. One such method is to take a common word and perform certain actions on it. Using the word Dinosaur as an example, users often create passwords such as DiNoSaUr (by alternating upper and lower case), rUaSoNiD (by reversing the string), oSNaiUDr (by shuffling the string), D9n6s7u3 (combining numbers and letters). However, the better the password is, the harder it is to remember.

Another drawback of alpha-numeric password is the dictionary attack. Because of the difficulty in remembering random strings of characters, most users tend to choose a common word,