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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 693
662
SECURITY
CHAP. 9
at a competitor’s factory and with no system administrator currently logged in.
If
the coast was clear, it would interfere with the production process, reducing prod-
uct quality, thus causing trouble for the competitor.
In all other cases it would do
nothing, making it hard to detect.
Another example of targeted malware is a program that could be written by an
ambitious corporate vice president and released onto the local LAN.
The virus
would check if it was running on the president’s machine, and if so, go find a
spreadsheet and swap two random cells. Sooner or later the president would make
a bad decision based on the spreadsheet output and perhaps get fired as a result,
opening up a position for you-know-who.
Some people walk around all day with a chip on their shoulder (not to be con-
fused with people with an RFID chip
in
their shoulder).
They have some real or
imagined grudge against the world and want to get even. Malware can help.
Many
modern computers hold the BIOS in flash memory, which can be rewritten under
program control (to allow the manufacturer to distribute bug fixes electronically).
Malware can write random junk in the flash memory so that the computer will no
longer boot.
If the flash memory chip is in a socket, fixing the problem requires
opening up the computer and replacing the chip.
If the flash memory chip is sol-
dered to the parentboard, probably the whole board has to be thrown out and a new
one purchased.
We could go on and on, but you probably get the point.
If you want more hor-
ror stories, just type
malware
to any search engine.
You will get tens of millions of
hits.
A question many people ask is: ‘‘Why does malware spread so easily?’’ There
are several reasons. First, something like 90% of the world’s personal computers
run (versions of) a single operating system, Windows, which makes an easy target.
If there were 10 operating systems out there, each with 10% of the market, spread-
ing malware would be vastly harder.
As in the biological world, diversity is a good
defense.
Second, from its earliest days, Microsoft has put a lot of emphasis on making
Windows easy to use by nontechnical people. For example, in the past Windows
systems were normally configured to allow login without a password, whereas
UNIX systems historically always required a password (although this excellent
practice is weakening as Linux tries to become more like Windows). In numerous
other ways there are trade-offs between good security and ease of use, and Micro-
soft has consistently chosen ease of use as a marketing strategy.
If you think secu-
rity is more important than ease of use, stop reading now and go configure your
cell phone to require a PIN code before it will make a call—nearly all of them are
capable of this.
If you do not know how, just download the user manual from the
manufacturer’s Website. Got the message?
In the next few sections we will look at some of the more common forms of
malware, how they are constructed, and how they spread. Later in the chapter we
will examine some of the ways they can be defended against.
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