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Unformatted text preview: now performs its intended function. Notice
that a virus spreads because every time an infected program is executed, it tries to
infect more programs. Also notice that a virus does not infect an already infected
file in order to prevent an object file from growing ever longer This allows the
virus to infect many programs without noticeably increasing disk space usage.
When a computer system suffers from virus infection, it has to be cured. Antivirus
utilities are often used to cure a computer from virus infection. These utilities first
identify the virus type with which the computer is infected by matching its marker
against the markers of well-known viruses. Once the type is known, the original programs are restored from their infected versions by applying a detailed
knowledge of the infection method used by the virus. For example, in viruses that
modify jump instructions at the beginning of the host program, recovering can be
done simply by restoring the original jump to the start of the host program code.
However, notice that these utilities can only cure specific known viruses. They
cannot cure a newly encountered type of virus. A good antivirus utility can
normally cure several hundred types of viruses and its power can be regularly
improved by frequently updating it as new viruses are discovered. SOME POPULAR OPERATING SYSTEMS
In this section we will have a look at some real operating systems that are in
popular use. The operating systems described are Unix, DOS, Windows, Windows
NT, and Linux. Many of these systems are continuously evolving. Therefore new
features keep getting added in their new versions. Hence instead of presenting a
detailed description of the features of each of these systems, only their overall
characteristics and some of their most interesting aspects have been presented.
Unix is a multi-user, time-sharing operating system. It is a very popular operating
system and can be used on a wide variety of computers ranging from notebook
computers to super computers. Although it can be...
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This document was uploaded on 04/07/2014.
- Spring '14