Passwords are everywhere in computer security. All too often, they are also ineffective. A good password has to be both easy to remember and hard to guess, but in practice people seem to pay attention to the former. Names of wives, husbands and children are popular. " 123456" or "12345" are also common choices. That predictability lets security researchers(and hackers)create dictionaries which list common passwords, useful to those seeking to break in. But although researchers know that passwords are insecure, working out just how insecure has been difficult. Many studies have only small samples to work on. However, with the co-operation of Yahoo!, Joseph Bonneau of Cambridge University obtained the biggest sample to date—70 million passwords that came with useful data about their owners. Mr Bonneau found some interesting variations. Older users had better passwords than young ones. People whose preferred language was Korean or German chose the most secure passwords: those who spoke Indonesian the least. Passwords designed to hide sensitive information such as credit-card numbers were only slightly more secure than those protecting less important things, like access to games. "Nag screens" that told users they had chosen a weak password made virtually no difference. And users whose accounts had been hacked in the past did not make more secure choices than those who had never been hacked. But it is the broader analysis of the sample that is of most interest to security researchers. For, despite their differences, the 70 million users were still predictable enough that a generic password dictionary was effective against both the entire sample and any slice of it. Mr Bonneau is blunt: "An attacker who can manage ten guesses per account will compromise around 1% of accounts. " And that is a worthwhile outcome for a hacker. One obvious solution would be for sites to limit the number of guesses that can be made before access is blocked. Yet whereas the biggest sites, such as Google and Microsoft, do take such measures, many do not. The reasons of their not doing so are various. So it' s time for users to consider the alternatives to traditional passwords.

单选题 People tend to use passwords that are______.

单选题 Researchers find it difficult to know how unsafe passwords are due to ______.

单选题 It is indicated in the text that______.

单选题 The underlined word "compromise" in Para. 5 most probably means______.

单选题 The last paragraph of the text suggests that______.