Malicious Mobile Code

Chapter 4. Viruses in a Windows World

This chapter builds on the knowledge learned in Chapter 3 by covering viruses and their effects on the Windows. It covers the effects of DOS viruses running under Windows and discusses viruses specifically created to infect Windows executables.

Tip

Internet scripting viruses will be covered in Chapter 8, Chapter 9, and Chapter 12.

DOS Viruses on Windows Platforms

In a PC world where Windows is king, there is still a significant population of functioning DOS viruses. They do not understand how to manipulate Windows executables and the newer file storage types, so their overall ability to spread on a Windows system is decreased in most cases. Still, some do work, and the ones that don’t, can still cause bootup and runtime errors. Under a DOS Virtual Machine (DVM) session, DOS is emulated well enough to allow most DOS viruses lots of opportunity to do damage.

Overall Effects on All Windows Platforms

This section will summarize the overall effects DOS viruses have on Windows, followed by specifics for each platform.

Boot virus infections

After the POST routine of a PC is finished, the first boot drive is checked, and the Master Boot Record (MBR) is located. The MBR then tells the PC where to locate the primary boot sector of the default operating system. This process is identical for every PC regardless of the operating system. Thus, a boot virus located on a booted floppy will be able to successfully infect the boot area of all hard drives. When an ...