Malicious Mobile Code

DOS Virus Technologies

After learning how to do it, the first thing a virus writer must do is decide what type of virus to write. A boot virus is often the choice because it loads before any other software and is in complete control before the operating system even gets loaded. File viruses are a little bit easier to write and can accomplish more. What either type can do is only limited by the virus writer’s creativity. He has to decide how obvious his bug will be, when it will spread, and what it will do when it decides to execute its payload.

Writing a Virus

Writing a virus isn’t as hard as most people think. You certainly don’t have to be a programming genius, as is popularly thought by most computer users. In fact, if all you do is write malicious code, then it’s easier than writing productive, legitimate applications. As a virus writer, the subset of applicable programming commands is smaller, and the time-consuming process of writing bulky error-checking routines can be thrown away. What they need to know is found in bland technical manuals filled with arcane detail. How else can you find out what track and sectors hold the disk partition table, or at what memory address DOS stores the interrupt vector table? Writing viruses takes as much patience as creativity.

Once the basic tenets of DOS and low-level programming are understood, writing a simple virus is straightforward. Don’t get me wrong. There are highly intelligent, gifted, malicious code writers in the world. Fortunately, ...