阅读下列短文，从每题所给的四个选项(A、B、C和D)中选出最佳选项。
By creating a distinctive username and reusing it on multiple websites，you may be giving online marketers and scammers a simple way to track you. Four researchers from The French National Institute for Research in Computer Science and Control (INRIA) studied over 10 million usernames－collected from public Google profiles，eBay accounts，and several other sources. They found that about half of the usernames used on one site could be linked to another online profile，potentially allowing marketers and scammers to build a more complex picture of the users.
“These results show that some users can be profiled just from their usernames，” says Claude Castelluccia，research director of the security and privacy research group at INRIA，and one of the authors of a paper on the work.“More specifically，a profiler could use usernames to identify all the profiles that belong to the same user，and then use all the information contained in these sites to profile the victim.”
Those who have more unique usernames are more likely to be attacked. The INRIA researchers have created a tool that can check how unique a username is，and thus how easily an attacker could use it to build a profile of a person.
Researchers are exploring ways that the traces of data that people leave on different websites could be combined and used to track them. A 2010 paper showed that the online groups to which people belonged could be used to infer their real identity in 42 percent of cases.
Building profiles of consumers using online information has already become a major industry for marketers as well as online criminals.
What would be the best title for the passage?

A．Look out for online criminals

B．Your username may betray you

C．Don't leave your traces online

D．A unique username is more attractive

Online marketers may use your username to ________.

A．get a picture of yours

B．steal from your online account

C．get useful information about you

D．find out your interest or hobbies

The main purpose of the passage is probably to ________.

A．warn us of the possible dangers of a unique username

B．tell us how to manage our online information

C．advise us on how to choose a proper username

D．tell us the importance of a username

We can infer from the passage that ________.

A．it's hard to build a profile of a person from an online username

B．it's better to use a more complex username online

C．an online username has little to do with the real person

D．we'd better not use the same username on different sites

The underlined word “scammers” in Paragraph 1 most probably means ________.

A．friends

B．criminals

C．victims

D．salesmen