填空题

The computer virus is an outcome of the computer overgrowth in
the 1980s. The cause of this term is the likeness between the biological
virus and the evil program infected with computers. The origin of this
term came an American science fiction "The Adolescence of P-1" written 62. ______
by Thomas J. Ryan published in 1977. Human viruses invade a living
cell and turn them into a factory for manufacturing viruses. 63. ______
Therefore, computer viruses are small programs. They replicate by attaching 64. ______
a copy of themselves to another program.
Once attached by host program, the viruses then look for other programs 65. ______
to" infect". In this way, the virus can spread quickly throughout a
hard disk or an entire organization. At some points, the situation will be 66. ______
totally determined by how the virus was programmed. The timing of the
attack can be linked to a number of situations, included a certain time 67. ______
or date, the presence of a particular file, the security privilege level of
the user and the number of times a file is used. So-called" benign" viruses
might simply display a message, like the one that infected IBM’s
main computer system last Christmas with a season’s greeting. Malignant
viruses are designed to damage the system. The attack is to wiping 68. ______
out data, to delete files or to format the hard disk.
There are two main types of viruses: shell and intrusive system.
Shell viruses wrap themselves around a host program and don’t modify
the original program. Shell programs are easy to write, that is why about 69. ______
half of viruses are of this type. Intrusive viruses invade an existing program
and actual insert a portion of themselves into the host program. 70. ______
Intrusive viruses are hard to write and very difficult to remove with 71. ______
damaging the host file.