Macworld — An attacker who wants to break into one of your accounts manually might first try likely passwords such as your pet's name, your anniversary, or other terms that are significant to you. If that doesn't produce results quickly, a hacker might turn to a program that rapidly tries each of the thousands or even millions of words in a big list--a procedure known as a dictionary attack. Some dictionary attacks are quite clever, checking not only common English terms but also foreign words, common misspellings, words in which letters have been replaced by numbers or symbols (such as @ppl3 for Apple), and easy-to-type sequences of characters, such as poiuytre.

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If that doesn't work, and if someone has the time and motivation, the next step would be a brute-force attack. In this type of attack, a computer program tries every possible combination of characters until the password is found, although current technology puts practical limits on the extent of such attacks.

When you create a new password, the trick is to come up with something that a dictionary attack could never discover, and to make the password long enough and complex enough that even a brute-force attack couldn't succeed because it would require too much time and processing power. Here's how:

Make them long

Passwords become exponentially harder to crack with each character you add, so longer passwords are much better than shorter ones. A brute-force attack can easily defeat a password with seven or fewer characters. Your mandatory minimum should be eight characters. Even then, you need to make those eight characters count: a randomly generated eight-character password using letters, numbers, and symbols (for example, h7%R9#jA) is vastly more secure than an ordinary eight-letter word such as licenses. You'll get the best protection from a random password of at least 11 characters or a non-random password of at least 17 characters (make sure that the password is not discoverable in any dictionary).

Start with a sentence

True mathematical randomness is hard to come by, but for a run-of-the-mill password, what counts is that a computer couldn't discern obvious or personal patterns in it. One common way to create a random password is to turn a sentence that you can easily remember into a password by using the first letter of each word, perhaps substituting some numbers as appropriate. The string ZTwt12potUS, as it follows no apparent pattern, might be a good choice. But it's still quite memorable because I derived it from the sentence "Zachary Taylor was the twelfth president of the United States."

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