Viruses
What type of programs can be infected?
The most important thing to note about viruses is that in order to infect a computer,
their code must be run or "executed". Files that are not programs, such as data files should
be immune from viruses. This has led to much misinformation about what can become infected.
The problem is that data files can have executable code in the form of macros or scripts.
And what about email? Surely, they should be safe. Not so. Modern email can be written in
the page description language of the world wide web, HTML. This can also harbor executable
scripts.
What can be infected?
- Files that are programs. These have the extension .com or .exe.
- Files that are parts of programs. These include overlays and the ever popular dynamic link layer
(.DLL) files.
- Programs that run within programs. Macros are a good example and can be found in all the
Microsoft programs.
- Script files. Visual Basic script (VBS) files can be executed within Microsoft programs and is
a popular method of using Outlook to spread viruses.
- Boot files. These are the programs that are used to start up the operating system.
- System areas of floppy diskettes and the hard disk. The system area of a hard disk is called the
master boot record. The system area can contain a small program.
- Computer memory.
- Data files that contain macros
- Program files that masquerade as non-programs such text, image, sound or video files. For example,
a file may be named song.mp3.exe. Since Microsoft's Windows Explorer normally hides the final
extension, in this case .exe. You think the file is called song.mp3, click on it and your computer
is infected.
What can't be infected?
- Data files such as images, sound and video as well as simple text files.
- In theory, data files should be immune to infection. However, if the data files contain small
programs, known as macros, they can harbor viruses. Microsoft's Office program is a well-known example of this.
- Text, images, sound and video files cannot contain a virus. However, if a program is disguised
as one of these files, it can contain a virus.
