单选题 Two decades ago only spies and systems administrators had to worry about passwords. But today you have to enter one even to do humdrum things like turning on your computer, downloading an album or buying a book online. No wonder many people use a single, simple password for everything.
Analysis of password databases, often stolen from websites, shows that the most common choices include "password", "123456" and "abc123". But using these, or any word that appears in a dictionary, is insecure. Even changing some letters to numbers ("e" to "3", "i" to "1" and so forth) does little to reduce the vulnerability of such passwords to an automated "dictionary attack", because these substitutions are so common. The fundamental problem is that secure passwords tend to be hard to remember, and memorable passwords tend to be insecure.
Weak passwords open the door to fraud, identity theft and breaches of privacy. An analysis by Verizon, an American telecoms firm, found that the biggest reason for successful security breaches was easily guessable passwords. Some viruses spread by trying common passwords.
The solution, say security researchers, is to upgrade the software in people's heads, by teaching them to choose more secure passwords. One approach is to use passphrases containing unrelated words, such as "correct horse battery staple", linked by a mental image. Passphrases are, on average, several orders of magnitude harder to crack than passwords. But a new study by researchers at the University of Cambridge finds that people tend to choose phrases made up not of unrelated words but of words that already occur together, such as "dead poets society" . Such phrases are vulnerable to a dictionary attack based on common phrases taken from the Internet. And many systems limit the length of passwords, making a long phrase impractical.
An alternative approach, championed by Bruce Schneier, a security guru, is to turn a sentence into a password, taking the first letter of each word and substituting numbers and punctuation marks where possible. "Too much food and wine will make you sick" thus becomes "2mf&wwmUs". This is no panacea: the danger with this "mnemonic password" approach is that people will use a proverb, or a line from a film or a song, as the starting point, which makes it vulnerable to attack.
Some websites make an effort to enhance security by indicating how easily guessed a password is likely to be, rejecting weak passwords, ensuring that password databases are kept properly coded and limiting the rate at which login attempts can be made. More should do so. But don't rely on it happening. Instead, beef up your own security by upgrading your brain to use mnemonic passwords.

单选题 The influence of substitution of letters for numbers in simple password is ______.
A. tremendous B. little
C. common D. obvious

单选题 It can be inferred from the study by Verizon that ______.
A. easy passwords make cheating possible
B. invasion of privacy is mainly caused by weak passwords
C. security breaches can be reduced by using safer passwords
D. the viruses are spread because of using common passwords

单选题 The research of the University of Cambridge shows people are inclined to use passphrases ______.
A. composed of words between which there is no connection
B. comprised by words that have already appeared together
C. that can be found on the Internet
D. that can be unlimited long

单选题 It is implied in the passage that the example of mnemonic password is ______.
A. "password" B. "correct horse battery staple"
C. "dead poets society" D. "2mf&wwmUs/

单选题 Which of the following is NOT the measure that more websites should take to improve security according to the last paragraph?
A. To upgrade mental software. B. To show the easiness to guess passwords.
C. To refuse to use the simple passwords. D. To restrict the times of login attempts.