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）处填（）。
A．virtual
B．virus
C．worms
D．bacteria