New subject: The first trustworthy <wink> GBayes results

28 Aug 2002


      Don't count words multiple times, and you'll probably
get fewer false positives.  That's the main reason I
don't do it-- because it magnifies the effect of some 
random word like water happening to have a big spam
probability. (Incidentally, why so high?  In my db it's 
only 0.3930784.)  --pg

--Tim Peters wrote:
...
FYI.  After cleaning the blatant spam identified by the classifier out of my
ham corpus, and replacing it with new random msgs from Barry's corpus, the
reported false positive rate fell to about 0.2% (averaging 8 per each batch
of 4000 ham test messages).  This seems remarkable given that it's ignoring
headers, and just splitting the raw text on whitespace in total ignorance of
HTML & MIME etc.
'FREE' (all caps) moved into the ranks of best spam indicators.  The false
negative rate got reduced by a small amount, but I doubt it's a
statistically significant reduction (I'll compute that stuff later; I'm
looking for Big Things now).
Some of these false positives are almost certainly spam, and at least one is
almost certainly a virus:  these are msgs that are 100% base64-encoded, or
maximally obfuscated quoted-printable.  That could almost certainly be fixed
by, e.g., decoding encoded text.
The other false positives seem harder to deal with:
+ Brief HMTL msgs from newbies.  I doubt the headers will help these
  get through, as they're generally first-time posters, and aren't
  replies to earlier msgs.  There's little positive content, while
  all elements of raw HTML have high "it's spam" probability.
Example:
"""
--------------=_4D4800B7C99C4331D7B8
Content-Description: filename="text1.txt"
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable
Is there a version of Python with Prolog Extension??
Where can I find it if there is?
Thanks,
Luis.
P.S. Could you please reply to the sender too.
--------------=_4D4800B7C99C4331D7B8
Content-Description: filename="text1.html"
Content-Type: text/html
Content-Transfer-Encoding: quoted-printable
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML>
<HEAD>
        <TITLE>Prolog Extension</TITLE>
        
        
        
        
</HEAD>
<BODY>
<PRE>Is there a version of Python with Prolog Extension??
Where can I find it if there is?
Thanks,
Luis.
P.S. Could you please reply to the sender too.</PRE>
</BODY>
</HTML>
--------------=_4D4800B7C99C4331D7B8--"""
"""
Here's how it got scored:
prob = 0.999958816093
prob('
Note that '
+ Msgs talking *about* HTML, and including HTML in examples.  This one
  may be troublesome, but there are mercifully few of them.
+ Brief msgs with obnoxious employer-generated signatures.  Example:
"""
Hi there,
I am looking for you recommendations on training courses available in the UK
on Python.  Can you help?
Thanks,
Vickie Mills
IS Training Analyst
Tel:    0131 245 1127
Fax:    0131 245 1550
E-mail:    vickie_mills@standardlife.com
For more information on Standard Life, visit our website
http://www.standardlife.com/   The Standard Life Assurance Company, Standard
Life House, 30 Lothian Road, Edinburgh EH1 2DH, is registered in Scotland
(No SZ4) and regulated by the Personal Investment Authority.  Tel: 0131 225
2552 - calls may be recorded or monitored.  This confidential e-mail is for
the addressee only.  If received in error, do not retain/copy/disclose it
without our consent and please return it to us.  We virus scan all e-mails
but are not responsible for any damage caused by a virus or alteration by a
third party after it is sent.
"""
The scoring:
prob = 0.98654879055
prob('our') = 0.928936
prob('sent.') = 0.939891
prob('Tel:') = 0.0620155
prob('Thanks,') = 0.0337316
prob('received') = 0.940256
prob('Tel:') = 0.0620155
prob('Hi') = 0.0533333
prob('help?') = 0.01
prob('Personal') = 0.970976
prob('regulated') = 0.99
prob('Road,') = 0.01
prob('Training') = 0.99
prob('e-mails') = 0.987542
prob('Python.') = 0.01
prob('Investment') = 0.99
The brief human-written part is fine, but the longer boilerplate sig is
indistinguishable from spam.
+ The occassional non-Python conference announcement(!).  These are
  long, so I'll skip an example.  In effect, it's automated bulk email
  trying to sell you a conference, so is prone to use the language and
  artifacts of advertising.  Here's typical scoring, for the TOOLS
  Europe '99 conference announcement:
prob = 0.983583974285
prob('THE') = 0.983584
prob('Object') = 0.01
prob('Bell') = 0.01
prob('Object-Oriented') = 0.01
prob('**************************************************************') =
0.99
prob('Bertrand') = 0.01
prob('Rational') = 0.01
prob('object-oriented') = 0.01
prob('CONTACT') = 0.99
prob('**************************************************************') =
0.99
prob('innovative') = 0.99
prob('**************************************************************') =
0.99
prob('Olivier') = 0.01
prob('VISIT') = 0.99
prob('OUR') = 0.99
Note the repeated penalty for the lines of asterisks.  That segues into the
next one:
+ Artifacts of that the algorithm counts multiples instances of "a word"
  multiple times.  These are baffling at first sight!  The two clearest
  examples:
"""
...
...
Can you create and use new files with dbhash.open()?
Yes. But if I run db_dump on these files, it says "unexpected file type
or format", regardless which db_dump version I use (2.0.77, 3.0.55,
3.1.17)
It may be that db_dump isn't compatible with version 1.85 databse files.  I
can't remember.  I seem to recall that there was an option to build 1.85
versions of db_dump and db_load.  Check the configure options for
BerkeleyDB to find out.  (Also, while you are there, make sure that
BerkeleyDB was built the same on both of your platforms...)
...
...
Try running db_verify (one of the utilities built
when you compiled DB) on the file and see what it tells you.
There is no db_verify among my Berkeley DB utilities.
There should have been a bunch of them built when you compiled DB.  I've got
these:

Re: RE: [Python-Dev] The first trustworthy <wink> GBayes results

Paul Graham

Tim Peters

Tim Peters

Anthony Baxter

Skip Montanaro

Anthony Baxter

barry＠python.org

tags

participants (5)