48 Can boot sector viruses infect non-bootable DOS floppy disks?
Description
This article is from the Computer Viruses FAQ, by Nick FitzGerald n.fitzgerald@csc.canterbury.ac.nz with numerous contributions by others.
48 Can boot sector viruses infect non-bootable DOS floppy disks?
Any DOS diskette that has been properly formatted contains some
executable code in its boot sector. (There is some debate as to whether
this code should be called a program or not. The important thing here
is that this code is *executed* at system startup if the diskette is in
the system's boot drive.) If a diskette is not "bootable", all that
boot sector (normally) does is print a message (on a PC, typically
something like "Non-system disk or disk error; replace and strike any
key when ready"). However, the boot sector is still executable and
therefore vulnerable to infection. Should you accidentally boot your
machine with a "non-bootable" diskette in the boot drive, and see that
message, it means that any boot virus that may have been on that
diskette *has* run, and had the chance to infect your hard drive, or
whatever. So, when talking about viruses, the words "bootable" and "non-
bootable" are misleading. All formatted diskettes are capable of
carrying boot sector viruses.
Most current computers will try to boot from their (first) floppy drive
before trying to load an operating system off their hard disks. Because
of this and the fact that every floppy disk is possibly infected with a
boot sector virus, it is a *very* good idea to set your computer to try
to boot from its hard disk. Many newer PCs offer the option to select
boot order in their system CMOS setup routines. If your computer has
such an option, set it to try to boot from your hard disk first.
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