programming-for-dummies

Dissecting Programs with a Disassembler 105
Book I
Chapter 4
Figure 4-10:
An installer
lets you
define
which files
to copy and
where to
store them
on a hard
disk.
Programming Tools
Dissecting Programs with a Disassembler
A disassembler acts like a reverse compiler. A compiler converts your program
(written in any programming language, such as C++ or Pascal) into
machine language, a disassembler takes an executable file (which contains
machine language code) and converts it into assembly language.
Disassemblers can’t convert machine language back into its original source
code language (such as C++) because disassemblers can’t tell which programming
language was originally used. An executable file created from a C++ program
looks no different than an executable file created from a Pascal or BASIC
program. Therefore, disassemblers simply convert machine language into
assembly language.
Disassemblers have both honorable and shady uses. On the honorable side,
antivirus companies use disassemblers to dissect how the latest viruses,
worms, and Trojan Horses work. After they know how these nasty programs
work, they can figure out how to detect, stop, and remove these malicious
programs.
On the shady side, many companies use disassemblers to tear apart their rival’s
products and see how they work. After you know how a competitor’s program
works, you can copy those features and use them in your own program.