On Tue, 25 Nov 2003, Robert Menschel wrote:
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> Hello Aaron,
>
> Tuesday, November 25, 2003, 8:58:58 AM, you wrote:
>
> AY> ... Recently I started getting a lot of false positives with SA 2.60.
> AY> I noticed that all my mail was getting a bayesian score of 99 to
> AY> 100%. ...My best guess is that since the bayes database only holds a
> AY> limited number of tokens, my DB was filling up with spam tokens and
> AY> not enough non-spam tokens. Maybe this happened because I only get
> AY> about 10-20 legitimate emails a week versus about 100+ spam emails a
> AY> day.
>
> In November to date, I've trained my Bayes on 683 ham and 6816 spam.
> Ratio therefore seems to be about the same as yours. I haven't seen any
> evidence of the problem -- Bayes is working wonderfully here.
>
> Bob Menschel
Having had an experience similar to Aaron's I can believe that he could
be having problems with a poisoned Bayes. For example, suppose that you've
received a large number of "Nigerian" spams that were learned as such.
That would put spam scores on a large number of converstational words.
In a fit of pique, I had tossed a whole bunch of "Nigerian" spams in
my bayes. It got so bad that a test email that contained only one word
("Hi") got a Bayes 99% spam score. I had to trash the DB and start from
scratch.
So the quality of Bayes scoring does depend upon how it is trained.
It is a tool not a magic bullet, and like any tool can be misused
or abused. Spammers seem to be learning this, I'm seeing an increasing
number of spams that contain "Bayes poison".
Dave
--
Dave Funk University of Iowa
<dbfunk (at) engineering.uiowa.edu> College of Engineering
319/335-5751 FAX: 319/384-0549 1256 Seamans Center
Sys_admin/Postmaster/cell_admin Iowa City, IA 52242-1527
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