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\section{Micro Computers}

While the bulk of this book and class has concerned multi-user
computers on networks, micro computers are also worth some attentions. 

Basically there are four issues that cause concern.

\begin{description}

\item[Shared Disks.]  In many settings, micro computers are shared
among many users.  Even if each user brings his own data, often the
system programs are shared on communal hard-disk, network or library
or floppies.  This means that a single error can damage the work of
many people.  Such errors might include destruction of a system
program, intentional or accidental modification of a system program or
entry of a virus.

To combat this, systematic checking or reinstallation of software from
a known protected source is recommended.  In most shared facilities,
refreshing the network, hard-disk or floppy-library weekly should be
considered.  Shared floppies should be write protected and the original
copies of programs should be kept under lock and key and used only to
make new copies.

Trusted server the provide read only access to the system files have
been successfully used in some universities.  It is absolute critical
that these machines be used only as servers.


\item[Viruses.]  A number of computer viruses have been found for
micro-computers.  Many experts consider this problem to be practically
solved for Macintoshes an soon to be solved for IBM-style PC's. 

Two basic types of anti-viral software are generally available.  The
first type is installed into the operating and watches for virus's
trying to infect a machine.  Examples of this on the Mac include
Semantic's  SAM (Part 1), Don Brown's  vaccine and Chris Johnson's
Gate Keeper.

The second type of anti-viral software scans the disk to detect and
correct infected programs.  On the Mac,	SAM (Part 2), H. G. C.
Software's Virex, and John Norstab's Disinfinct are commonly used disk
scanners.

On the PC type of machines we find three types of virus.  The first of
these is a boot sector virus that alters the machine language start up
code found on the diskette.  The second infects the {\tt command.com} startup
file and the third alters the {\tt exe} (machine language executable files).


Flu Shot Plus by Ross Greenberg is an example of a program to deal
with {\tt command.com} \& some {\tt exe} virus.  Novirus and
cooperatively built by  Yale, Alemeda and Merit is one of the boot
track repair systems.

There are a number of electronic discussion groups that deal with
computer virus.  On BITNET (and forwarded to other networks),
{\tt virus-l} supports discussion about PC and Mac virus, while
{\tt valert} is used to announce the discovery of new ones. 
Compuserve's {\tt macpro} serves as a forum to discuss Macintosh viruses.

\item[Network.]  The third is issue is the placement of single user
computers on networks.  Since there is little or no authentication on
(or of) these machines, care must be taken to not place sensitive
files upon them in such a configuration.

\item[Reliability.]  Finally there is a reliability issue.  Most single
user computers were never designed for life and time critical
applications.  Before using such a computer in such an application,
expert advise should be sought.

\end{description}

In the use of single user computers, there are some basic issues that
need be considered and some simple advice that should be given. 


In the advice column, there are a few basic points.
\begin{enumerate}
\item Where
practical,  each user should have his own system disks and hence be
partially insulated from potential mistakes.

\item When people are sharing disks have an explicit  check out policy
logging the users of each disk.  Be sure to set the write-protect them
and teach the users how to write protect there own system disks.
(Most PC programs are sold on write-protected disks, this is not true
of most Macintosh programs.
\item Keep a back up copy of all system programs and system programs
to allow for easy restoration of the system.
\item Write lock originals and keep them under lock and key for
emergency use only.
\item Have an explicit policy and teach users about software theft and
software ethics.
\item Teach users to back up their data.  Just as with large
computers, the only real defense from disaster is redundancy.
\end{enumerate}

Even when the computer center is not providing the machines themselves, it
should generally help to teach users about backups, write protection,
software ethics and related issues.  Most PC users do not realize that
they are their own system managers and must take the responsibility of
care for their systems or risk the consequences.