D2) Is it possible to protect a computer system with only software?

Not perfectly; however, software defenses can significantly reduce
your risk of being affected by viruses WHEN APPLIED APPROPRIATELY.
All virus defense systems are tools - each with their own capabilities
and limitations.  Learn how your system works and be sure to work
within its limitations.

>From a software standpoint, a very high level of protection/detection
can be achieved with only software, using a layered approach.

1)  ROM BIOS - password (access control) and selection of boot disk.
    (Some may consider this hardware.)

2)  Boot sectors - integrity management and change detection.

3)  OS programs - integrity management of existing programs,
    scanning of unknown programs.  Requirement of authentication
    values for any new or transmitted software.

4)  Locks that prevent writing to a fixed or floppy disk.

As each layer is added, invasion without detection becomes more
difficult.  However complete protection against any possible attack
cannot be provided without dedicating the computer to pre-existing or
unique tasks.  The international standardization of the world on the
IBM PC architecture is both its greatest asset and its greatest
vulnerability.


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