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.

（73）处填（）。

A．memory

B．caches

C．ports

D．registers

( )使用同步(如在线交流)和异步(线程化讨论)手段使建设项目参与各方结合一定的工作流程进行协作和沟通。

A．建设项目协同工作层

B．个性化设置层

C．工作流支持层

D．数据安全层