Melissa and LoveLetter made use of the trust that exists between friends or colleagues.Imagine receiving an （） from a friend who asks you to open it. This is what happens with Melissa and several other similar email （） . Upon running, such worms usually proceed to send themselves out to email addresses from the victim’s address book, previous emails, web pages （） . As administrators seek to block dangerous email attachments through the recognition of well-known （） , 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 （） access to your network.

simultaneously runs commands in the background to steal your passwords and give the （） access to your network.

A．cracker

B．user

C．customer

D．client

某工务段养路工兼巡道工甲，为了排斥巡道工乙，以使自己能递升为正式巡道工，增加工资，多得奖金，因而故意把方头道钉一枚横插入钢轨接缝处，企图造成事故，嫁祸于乙，使某次列车险些脱轨倾覆。甲的行为构成（）。

A.破坏交通工具罪既遂

B.破坏交通工具罪未遂

C.破坏交通设施罪既遂

D.破坏交通设施罪未遂