Noncryptographic Security Issues - Codes: The Guide to Secrecy from Ancient to Modern Times - page 397

Virus Targets
Viruses may infect any of the following:
1. Executable Program Files :An executable program is a set of instructions
that can be input to the memory of a computer and executed. In other
words, it is a program that may be run as a self-contained procedure,
which consists of a main program and, possibly, one or more subprograms.
Usually, the name of such a program is all that is required to run it, merely
the typing in of the program name and requesting that the computer run
it.
2. File Directories : A computer's file-directory system keeps track of the
location of data files, and without them the computer will not function.
3. Macros : Today virus programs can be written so that, for instance, it may
attach itself to a macro 10.21 and is launched whenever the macro is run.
When we discuss “macro viruses” later, we will see that Microsoft Word
(MS-Word), documents are virtually always the target since they contain
programs, the macro language, which are automatically executed when
one of these “data” files is opened.
4. System Sector 10.22 : The system sector refers to special areas on the
computer's hard drive containing programs that are executed when the
computer is booted. These are not files, but rather small segments of the
hard disk that the hardware reads as a single unit. The system sector is
required for the normal functioning of the computer, even though they are
invisible to normal programs. Sometimes this is called the boot sector . 10.23
How Viruses Work : When an infected program is run, the first action is
to invoke the virus program and run it, since this is the first instruction line
of the controlling program. The second instruction is for the virus program to
check to see if the program it is about to infect has already been infected or not.
The mechanism by which this is accomplished is a message, called a v-marker
or virus marker , which the virus program places in the legitimate program.
10.21 A macro is a collection of instructions stored in an executable form, usually written to
automate a few steps. Macros may be application-specific, such as a word-processing macro
that executes certain steps within that program; or general-purpose, such as a keyboard
macro that types in a user's login name when a specific short sequence of keys is pressed on
the keyboard.
10.22 A sector is one of the areas (or “pie slices”), into which the disk is segmented. This
division of the disk into pie slices is the method of organizing it for access of data to the read-
write heads of the disk drive. Moreover, the disk is further divided into concentric circles, so
that a given area can be located via the intersection of a given sector and the concentric track
passing through it. There are further subdivisions of the tracks into what are called clusters ,
which are the storage units (usually 256 or 512 byte-lengths, which are minimal in terms of
allowing the unit to be addressable).
10.23 To boot a computer, also called booting up , is the action of loading an OS into the com-
puter's main memory (RAM), see Footnote 9.15 on page 346. On a large computer or a
mainframe, booting is sometimes called initial program load (IPL). To reboot is to reload, or
in the case of larger machines, to re-IPL .