选择题 .  Melissa and LoveLetter 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 e-mail     72    . Upon running, such worms usually proceed to send themselves out to e-mail addresses from the victim's address book, previous e-mails, web pages     73    .
    As administrators seek to block dangerous e-mail attachments through the recognition of well-known     74    , virus writers use other extensions to circument 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.71.