某学生忘记了自己的QQ号，但记得QQ号是由一个2，一个5，两个8组成的四位数，于是用这四个数随意排成一个四位数，输入电脑尝试，那么他找到自己的QQ号最多尝试次数为（　　）

A．18

B．24

C．6

D．12

Melissa and Love Letter made use of the trust that exists between friends or colleagues.　Imagine receiving an (71) from a friend who asks you to open it.　This is what happens with Melissa and several other similar email (72) .Upon　running ,such worms usually proceed to send themselves out to email addresses from the victim’s address book, previous emails, web pages (73) .

　　As administrators seek to block dangerous email attachments through the recognition of well-known (74) ,virus writers use other extensions to circumvent such protection.　Executable (.exe) files are renamed to .bat and .cmd plus a whole list of other extensions and will still run and successfully infect target users.

　　Frequently ,hackers try to penetrate networks by sending an attachment that looks like a flash movie ,which, while displaying some cute animation ,simultaneously runs commands in the background to steal your passwords and give the (75) access to your network.

72（）

A．virtual　

B．virus　

C．worms　　

D．bacteria