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Modern Operating Systems by Herbert Bos and Andrew S. Tanenb...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf
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Modern Operating Systems by Herbert Bos and Andrew...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 723
692
SECURITY
CHAP. 9
Viruses do not have to passively lie around waiting for an antivirus program to
kill them, like cattle being led off to slaughter. They can fight back.
A particularly
exciting battle can occur if a memory-resident virus and a memory-resident
antivirus meet up on the same computer. Years ago there was a game called
Core
Wars
in which two programmers faced off by each dropping a program into an
empty address space. The programs took turns probing memory, with the object of
the game being to locate and wipe out your opponent before he wiped you out. The
virus-antivirus confrontation looks a little like that, only the battlefield is the ma-
chine of some poor user who does not really want it to happen there. Worse yet, the
virus has an advantage because its writer can find out a lot about the antivirus pro-
gram by just buying a copy of it. Of course, once the virus is out there, the
antivirus team can modify their program, forcing Virgil to go buy a new copy.
Virus Avoidance
Every good story needs a moral. The moral of this one is
Better safe than sorry.
Avoiding viruses in the first place is a lot easier than trying to track them down
once they have infected a computer. Below are a few guidelines for individual
users, but also some things that the industry as a whole can do to reduce the prob-
lem considerably.
What can users do to avoid a virus infection?
First, choose an operating sys-
tem that offers a high degree of security, with a strong kernel-user mode boundary
and separate login passwords for each user and the system administrator. Under
these conditions, a virus that somehow sneaks in cannot infect the system binaries.
Also, make sure to install manufacturer security patches promptly.
Second, install only shrink-wrapped or downloaded software bought from a re-
liable manufacturer. Even this is no guarantee since there have been cases where
disgruntled employees have slipped viruses onto a commercial software product,
but it helps a lot. Downloading software from amateur Websites and bulletin
boards offering too-good-to-be-true deals is risky behavior.
Third, buy a good antivirus software package and use it as directed.
Be sure to
get regular updates from the manufacturer’s Website.
Fourth, do not click on URLs in messages, or attachments to email and tell
people not to send them to you. Email sent as plain ASCII text is always safe but
attachments can start viruses when opened.
Fifth, make frequent backups of key files onto an external medium such as
USB drives or DVDs. Keep several generations of each file on a series of backup
media. That way, if you discover a virus, you may have a chance to restore files as
they were before they were infected. Restoring yesterday’s infected file does not
help, but restoring last week’s version might.
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