[Magictour] Re: pandiagonal

John Beasley, in an afterthought to a recent e-mail writes:

Here's a thought. A pan-diagonal nxn square must satisfy 4n constraints,
which goes up linearly with n. The number of knight's tours on an nxn board
goes up (I would think) by something not too far short of factorial-n. Does
there exist a suitably huge N such that a knight's tour forming a
pan-diagonal magic square is possible?

JDB

He also sends the following views on virus protection. Is he paranoid or am
I cavalier in relying on Norton with automatic update?

Viruses
=======

John Beasley's start-from-square-one approach to virus avoidance.

Observation 1: the really dangerous virus is the latest one, which has been
released since the most recent update of the virus detection software.

Observation 2: the time taken for the virus detection people to identify a
new virus and get an updated checker into the hands of the public is
T1+T2+T3, where

- T1 is the time between the release of the virus and the arrival of a copy
at the virus detection lab;

- T2 is the time for the virus detection people to work out what it is and
to update their checker;

- T3 is the time for the updated checker to get into the hands of the lab's
customers.

In practice, T2 appears to be typically between 3 and 12 hours. However,
even if T2 could be reduced to zero, we would still have to contend with T1
and T3, and in the event of a successful virus which severely degrades
Internet commmunication T3 may be quite long.

Conclusion: the only **truly** secure way to avoid infection is to place
all files which are capable of harbouring viruses into quarantine for at
least 24 and preferably 48 hours, to check in the ordinary news media that
there has been no report of a spectacularly successful virus which might
have significantly affected T3, and **only then** to download the latest
virus checker and examine them.

This degrades e-mail to below snail-mail standards, and is not a realistic
way of working. Additionally, people who work alone have to answer the
question: which will cost more time, regularly to download and install
virus-checker updates, or simply to avoid all files which might give
trouble?

Given that (a) my incoming mail is small and (b) only 48-hour quarantine
plus interrogation of the news media appears to guarantee complete security,
I have decided on the latter approach, and only files which are physically
incapable of harbouring viruses are opened. People who send me material for
my benefit are asked to respect this, and only to send me files which are
intrinsically safe (Word documents sent for my benefit are opened by Notepad
as if they were text files, and the substantive text located and extracted
without regard to any fonting or formatting). People who send material for
their own benefit are given no option, and anything potentially harmful is
destroyed unopened. **I DO NOT REGOGNIZE ***ANYONE*** AS A TRUSTED
SOURCE.** It is a property of a competently written virus that the victim
passes it on before he realises that he has acquired it, and I do not
believe that any person or organization can be expected to observe the
quarantine periods and other inconveniences necessary for complete security.

JDB, March 2001 (slightly revised October 2002)




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Received on Thu Dec 04 14:24:18 2001