The Risks Digest

The RISKS Digest

Forum on Risks to the Public in Computers and Related Systems

ACM Committee on Computers and Public Policy, Peter G. Neumann, moderator

Volume 8 Issue 26

Wednesday 15 February 1989


o "$15 Million Computer Dud Baffles Udall"
Joseph M. Beckman
o Re: Computer blamed for 911 system crash
Rodney Hoffman
Paul Blumstein
o Selling who-called-the-800-number data
Bob Ayers
o PIN? Who needs a PIN?
Alan Wexelblat
o Door Sensors and Kids
Eddie Caplan
o Risks of misunderstanding probability and statistics
Tom Blinn
o Why you can't "flip" bits on a WORM disc
Daniel Ford
o Credit Checker & Nationwide SS# Locate
David Andrew Segal
o Re: Authenticity in digital media
Pete Schilling
o Re: multi-gigabuck information "theft"
Jeff Makey
o Info on RISKS (comp.risks)

"$15 Million Computer Dud Baffles Udall"

"Joseph M. Beckman" <Beckman@DOCKMASTER.ARPA>
Wed, 15 Feb 89 16:45 EST
Summarized from the Washington Times (2-15-89):  The US Office of Surface
Mining has spent some $15 million on a computer system to prevent strip mine
law violators from obtaining new permits.  The GAO is calling it a failure.
The system apparently has a high error rate because it uses lists of names and
addresses that are not complete.  Arizonia democrat "Mo" Udall was quoted as
saying "I'm really baffled.  We have computer systems in this country to keep
track of everything from missiles to kindergarten kids who are sick or absent.
But the Interior Department can't develop a system, even with the help of %15
million, to keep violators out of the coalfields."

By using the phrase "missiles to kindergarten kids" he seems to imply that
systems are handling things as complex as missiles to as simple as...  Of
course, the fact that the subjects of the systems may be very complicated says
nothing about what the system is actually doing.

Re: Computer blamed for 911 system crash — more (RISKS-8.24)

Rodney Hoffman <>
15 Feb 89 09:38:31 PST (Wednesday)
On Saturday, 11 Feb 89, the Los Angeles city emergency 911 telephone system
crashed twice.  The initial story, summarized in RISKS 8.24, blamed "a
power failure in the computer's signalling mechanism."  The `Los Angeles
Times' (14 Feb 89) carried a follow-up story by Frederick M. Muir and Paul
Feldman, with the following new information.

The crash was caused by one power converter board, an SL/1 positron switch,
that helps control power fed to a complex switching system.  It failed for
still unknown reasons.  It's an off-the-shelf part that involves a low
degree of technology and sells for $1000, according to Pacific Bell service
manager Mike Fink.  The switch recieves incoming 911 calls and routes them
virtually instantaneously to the first open phone line.

"Fink said the board that failed is usually so reliable and simple that no
backup was designed into the system.  It is virtually the only part of the
system — which cost $1.6 million to install — without a backup."

Asked for past failure statistics, Pacific Bell and General Telephone,
which between them operate hundreds of 911 systems across California,
reported only two other failures in the past two years, neither of which
was linked to the part which failed Saturday.

Computer blamed for 911 system crash — more (Re: RISKS-8.24) <Paul Blumstein>
Wed, 15 Feb 89 09:29:23 PST
... The Los Angeles 911 system has had continual overload problems since its
inception because it was expected that only 30-40% of emergency callers
would use the system.  The actual number turned out to be 75%.  In
addition, the system has received a large amount of non-emergency calls.

The overload has caused a several-minute delay during peak periods before a
911 operator could be reached.

Paul Blumstein, Citicorp/TTI, Santa Monica, CA 
{philabs,csun,psivax}!ttidca!paulb  or  paulb@ttidca.TTI.COM

Selling who-called-the-800-number data

Bob Ayers <>
Mon, 13 Feb 89 12:59:53 PST
Those that liked the idea of states selling driver info will really love
this one.  As reported in the 20 February Forbes magazine, a new company,
Strategic Information Inc ...

    will collect, analyze and resell information on everything from retail
    prices in grocery stores to the premiums charged by insurance
    companies ... [it] intends to offer custom tailoring of such data to
    meet the needs of individual clients ...

    One feature, available this spring through a 160-million-name database
    that Strategic recently purchased, will be marketed to companies with
    toll-free phone lines: For a fee, the companies can check the origins
    of any calls they receive through 800 numbers — even those that don't
    go through — enabling them to target the dialers for follow-up
    mailings or sales pitches.

PIN? Who needs a PIN?

Alan Wexelblat <>
Wed, 15 Feb 89 10:39:44 CST
Last night I had a rather frightening experience with my bankcard.  Using
one of the network of machines which is supposed to accept my card, I tried
to make a withdrawal.  The machine accepted my card, printed a message on
its screen saying "Hello Alan Wexelblat, welcome to 

Door Sensors and Kids

Wed, 15 Feb 89 16:42:36 EST
While reading back issues of RISKS, I ran across the discussion here about
automatic sensors for controlling doors.  This made me recall that when we
would bring our 2 year old son into work, he was not tall enough to trip the
electronic eyes on the elevator doors.  Subsequently, we always had to be sure
to hold the door until he passed through or he would get bonked.  The doors
never closed hard enough to cause him any serious damage, but that's the RISK
of the doors' hardware working properly.

Risks of misunderstanding probability and statistics

Dr. Tom @MKO, CMG S/W Mktg, DTN 264-4865 <>
15 Feb 89 08:37
As a person who has earned a doctorate in statistics, with emphasis on its
practical applications (although I no longer work in that field), I have been
both amused and appalled by some of the recent contributions focusing on
probabilistic and statistical analysis of the risks of aircraft engine failures.

Some of the contributions assume, for example, that there really is such a
thing as "the probability that one engine will fail", and that therefore you
can compute the probability that two engines will fail (assuming that the
failures are independent) by simply squaring this "p".  This is such an
incredibly simplistic way of looking at the problem that I'm amazed that anyone
would offer it for consideration.  Clearly, on any given aircraft, the engines
share some subsystems in common; for example, they draw fuel from a common
supply, possibly with a common fuel pump, possibly using two or more
independent pumps.  Certain failures in the common subsystems could cause both
(or all) engines to fail.  On the other hand, the engines have other subsystems
that are not shared.  While these unique subsystems may have been equivalent
(and thus, have a common propensity to fail) at the time of manufacture, they
almost certainly are not equivalent after any period of maintenance in the
field.  Consequently, even if we disregard the failures of common subsystems,
the remaining engines almost certainly don't share a common probability of
failure.  Assuming they do can be an interesting and useful strategem for
thinking about joint probability of failure, but it's a dangerous

In RISKS-FORUM Digest Volume 8 : Issue 24, it is asserted by Barry Redmond that

>If someone makes a mistake on one engine at any of these times, there is a
>high probability that they will make the same mistake on the other engine(s).

That may be true, but it may not be true, because the same person may not
be working on all the engines.  I would agree that an incompetent mechanic
working on all the engines is likely to make the same mistakes on all of
them, but the reality of aircraft engine repair is different.

>The probabilities of failure are not independent because if one engine fails it
>immediately increases the probability of another failing.

This is a very interesting assertion.  It seems to be saying that there is a
causal relationship between a first engine failure and the likelihood of a
second.  Now, I would agree that if I were on an aircraft where one engine had
just failed, I'd worry lots more that a second would fail as well then I
usually would worry about engine failure when no engines had failed, but this
doesn't mean that the probability of failure of the other engines has changed
in any way.  (It also doesn't mean that it hasn't, and if it has changed, it
could be less or greater.)

It's unfortunate that a thorough grounding in probability theory and in
statistical inference (and in risk analysis) isn't a part of the technical
curriculum.  Failures happen.  They usually are not independent.  Knowing how
to analyse the risks of failures can help in making the tough decisions about
where to put resources to "prevent" or "protect against" failures.

Dr. Thomas P. Blinn, Marketing Consultant, Application Platforms, 
U. S. Channels Sales, Digital Equipment Corporation, 
Continental Blvd. — MKO2-2/F10 Merrimack, New Hampshire 03054

  Opinions expressed herein are my own, and do not necessarily represent
  those of my employer or anyone else, living or dead, real or imagined.

Why you can't "flip" bits on a WORM disc

Daniel Ford <>
Wed, 15 Feb 89 11:23:41 EST
Some contributors have noted that there are risks in trusting the integrity of
data stored on indelible storage devices such as WORM type optical discs.
These types of devices are often employed to store archival data that is never
legitimately altered (bank records, school transcripts, transaction logs,
etc.).  There seem to be two risks to trusting this technology.  The first is
"How can you be sure that the disc you are reading is the original and not some
altered copy?" and the second was "How can you be sure that some bits have not
been 'flipped' by overwriting a disc sector with a new value that happens to
burn a pit in the right spot?" The first concern is valid, but the second is

There are two reasons for this.  Firstly, each disc sector on a WORM (and
other types of optical discs) disc is protected with a sophisticated error
correction code.  These codes are very robust and are used because the very
high storage densities of optical discs tend to give them correspondingly
high error rates.  So, if a bit (or several) was somehow "flipped", the ECC
would either "correct" the change or report a read error. 

The second reason has to do with how data is actually encoded on the disc
surface.  Contrary to what might first be thought, "pits" (the holes) and
"lands" (space in a track between pits) do not correspond directly to 1's and
0's.  Rather, their lengths and transitions form a sequence that encodes the
data.  Many codes have been developed, but a common one is NRZM (Non-return to
zero mark).  Basically, in this code the transitions between the lengths of
both pits and lands record sequences of 0's and the transitions between the two
record individual 1's.  Certain minimum and maximum lengths of pits and lands
must be respected for clocking and detection purposes.

In such a scheme, you cannot just flip one bit (by making a pit longer) you
must flip two or more.  So, even if you could get past the ECC, it would be
quite difficult to get something specific and meaningful (i.e. not some weird
control character in the middle of someone's name) by overwriting a WORM disc

Further, each sector overwrite will also overwrite the ECC and change its
encoded value, which is burned into the disc along with the data, to some
other value.  As such, it is unlikely that the ECC and the sector contents
will remain consistent after an overwrite (giving subsequent read errors).

It would be much easier to forge a disc and substitute it for the real thing
then try to alter the original.  But, safeguards against that can be developed
as well.
                                        Dan Ford

     [Thanks for the elaboration.  But remember that even if you have an
     N-error detecting code, many (N+1)-bit falsifications will go 
     undetected.  Similar problems exist with ECC.  PGN]

Credit Checker & Nationwide SS# Locate

David Andrew Segal <dasegal@brokaw.LCS.MIT.EDU>
Wed, 15 Feb 89 16:52:28 EST
A member of my research group received the following "comforting"
advertisement in the mail (comments in [] are my editorial remarks...):

                   just got

* Consumer Credit Reports from thousands of credit sources coast-to-coast.
* Social Security Number tracing anywhere in the country.
* Driver's License reports from every state but Massachusetts [See Risks 8.20]
* Financial reports on over 9,000,000 businesses all across the USA.

                   and now,
           offers an exciting NEW service: [oh, boy]


With NATIONAL ADDRESS/IDENTIFIER UPDATE you can enter either a name
and address or a Social Security Number.  The Network will search all
over the nation and get a complete report back to you in just seconds!

You can get such information as all current names, aliases, social
security numbers and/or variances, date of birth, present and past
employers and past and/or present addresses.

You can find people anywhere in the country without having to access a full
Credit Report.  No permissible purpose under the Federal Law is required to run
NATIONAL ADDRESS?IDENTIFIER UPDATE...and NO RECORD of an inquiry will be logged
on the consumer's credit report! ... [Boy, it isn't illegal and no one will
ever no you invaded their privacy!]


I think the ad says it all.
David Andrew Segal, MIT Laboratory for Computer Science

                             [And don't forget the on-line National Credit
                             Information Network mentioned in RISKS-8.11.  PGN]

Re: Authenticity in digital media (RISKS-8.25)

15 Feb 89 14:51:00 EST
Seeing hasn't been believing for a long time.  Remember Fred Astaire dancing on
the ceiling in the movie "Singing in the Rain"?  And the newsreel footage
showing Hitler dancing a little jig in front of the Eiffel Tower after the
French surrender in WWII was a good piece of 1940 film editing, not an accurate
motion picture.  Counterfeit paintings in the style of well-known artists have
been around for at least four hundred years.  The Shroud of Turin was recently
found to date from the 13th instead of the 1st century A.D.  Counterfeit coins
were a problem in Roman Empire.

Computers haven't cut us off from history.  They just provide new tools with
which human beings can fool one another.
                                             Pete Schilling, Alcoa Laboratories

Re: multi-gigabuck information "theft"

Jeff Makey <Makey@LOGICON.ARPA>
14 Feb 1989 2127-PST (Tuesday)
In RISKS DIGEST 8.23 Mark Brader <> paraphrases a recent
article from the Toronto Star:

>A password belonging to [a large Canadian] company was used to steal
>information which the company values at $4 billion (Canadian) ...

This report isn't news.  The "computer files" are nothing more than the source
code for AT&T's UNIX operating system, copies of which may be easily obtained
for a license fee on the order of a few thousand dollars — a far cry from $4
billion.  I suspect that AT&T's lawyers are at the root of this sensationalism.

Jeff Makey    

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