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四级练习2016.03.23


       
       



The computer virus is an outcome of the computer overgrowth in the 1980s. (1)__________________________________________________.The origin of this term came from an American science fiction "The Adolescence of P-1" written by Thomas J. Ryan, published in 1977. Human viruses invade a living cell and turn it into a factory for manufacturing viruses. However, computer viruses are small programs. They expand by attaching a copy of themselves to another program. Once attached to the host program, the viruses then look for other programs to "infect". (2)_________________________________.The timing of the attack can be linked to a number of situations, including a certain time or date, the presence of a particular file, the security level of the user, and the number of times a file is used. Likewise, the mode of attack varies. So called "benign" or the harmless viruses might simply display a message, like the one that infected IBM's main computer system last Christmas with a season's greeting.(3)______________________________________________.The attack is to wipe out data, to delete files, or to format the hard disk.



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