Whether you are logging on to your personal computer, using a credit card, or disarming a door security system, passwords or PINs(personal identification numbers) jealously guard access to numerous regular operations. It is estimated that within ten years, consumers could be faced with handling more than 100 passwords! Given the popularity of passwords, how can you choose ones that are sufficiently complicated to be secure yet are simple enough to remember? There are basic guidelines to bear in mind. First, don't use as a password your name or that of a member of your family, even in modified form. Also avoid use of your telephone number, your Social Security number, or your address. Such information can easily be obtained by a determined hacker (黑客). In addition, if possible, don't use passwords made up entirely of letters or digits. A relatively simple computer program can crack such a code quickly: Finally, do not use a word that can be found in any dictionary, even a foreign-language one. Huge lists are available that contain words, place names, and proper names from all languages. Programs can test for variations of these words, such as if they are spelled backward, capitalized, or combined. So, what kinds of passwords should be used? Usually ones that have a minimum of six to eight characters and that have a mixture of upper-and lower-case letters, digits, and punctuation (标点) symbols. How difficult is it to crack such a combination of characters? One source says that 'a machine that could try one million passwords per second would require, on the average, over one hundred years.' How can you choose a combination that is easy to remember? Some suggest that you take the title of a favorite book or film or a line from a song or poem and use the first latter from each word as your password, adding capital letters, punctuation, or other characters. For example, 'to be or not to be' could become '2B/not2B'. Other suggestions include taking two short words and link them with a punctuation character, such as 'High?Bug' or 'Song Tree'. Taking into account the suggestions outlined above can help you to protect important information from unwanted hackers. Remember, too, the importance of changing your passwords regularly. Just a final comment, whatever passwords you decide to use, don't pick any of the examples given above. What is the main idea of this passage?