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Tests previously of interest only to philosophers and artificial
intelligence theorists
are now being used to hinder the everyday evil
of spam email.
The brilliant English mathematician
Alan
Turing - instrumental in breaking
the Enigma code during World War II -
is widely regarded as one of the founders of modern computer
science (see "What
computers can't do" in Issue 5).
In a 1950 paper,
he described what he called the
Imitation game,
now known as the Turing
Test, in which a person (in a
separate room) tries
to distinguish between human and computer test subjects by
asking them each a series of questions. If the person
can't distinguish between the computer and the human, the computer
is deemed to be intelligent. There is a (currently unclaimed)
prize of
$100,000 for a computer that can pass the Turing Test.
By definition, the original Turing test requires a human being to
judge between the two candidates. However, researchers from the
Carnegie Mellon School of Computer Science have developed a
version of the test that dispenses with the human judge - the
"Completely
automated public turing test to tell computers and humans
apart", or CAPTCHA for short.
Plus CAPTCHA style!
CAPTCHA works by presenting an image of a word
that has been distorted and obscured
so that a computer is not able to recognise it, while a
human still can. For example, the text of the word "plus" on the
right
was skewed and placed on a patterned background,
before the image was
chopped up into a number of pieces. To pass the test, a candidate must
correctly type such a distorted word
(or number of words in some versions).
Spammers not only use robot programs to crawl the web looking for email
addresses to send spam mail to, but also use similar robots to
apply automatically
for free email addresses from which to send the spam.
Hotmail
and
Yahoo are
now preventing this by putting a CAPTCHA style
question in their standard registration forms. An applicant who can't
read the word doesn't get an email address. So the use of CAPTCHA
goes at least part of the way to stopping spammers.
It is nice to know
that in an age when computers seem to be so vulnerable to problems -
viruses, spam emails, security breaches - computers are now
beginning to police themselves, even if it is by failing Turing's
test for intelligence!
Further information on Alan Turing and the Turing Test:
The Alan Turing Home Page
The Turing Archive for the
History of Computing
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