Oracle Tips by Burleson
Chapter 13 - Spam, Spam,
Using Spam Control Programs
As might be expected, there are various
techniques employed by anti-spam programs to achieve the goal of
reducing spam. One method defines a list of words that are often
used in spam messages and then scans the incoming e-mail for those
words. If a message contains too many of the words on the list, the
message will be identified as spam and then dealt with accordingly.
A second method compiles a list of known spam senders and
automatically deletes any message received from a target address.
Both methods have their limitations. The word
list variation is particularly weak for two primary reasons. First,
the word list rule is extremely easy for spammers to get around.
All that is necessary to skirt the word list filter is to modify a
word in any way that obscures the ability of the filter to identify
it as a target word.
This is, in fact, the same method introduced
earlier as a way to make an e-mail address non-machine-readable.
For example, the sender of spam e-mail targeting dog owners may
choose to use the representation “d0gs” when the word dog is
intended. The meaning is clearly communicated, and the spam filter
cannot pick up the target word because it is not present. There are
thousands of variations on this theme that are used every day to
defeat word list spam filters.
The second primary weakness of the word list
filter method is that it is impossible to identify words that will
appear exclusively in spam messages. A spam message highlighting a
pornographic website may contain the word “breast.” A word list
spam filter configured to delete messages containing the target word
would indeed deal with the incoming spam; yet, it would also delete
a message regarding a local fundraising event for breast cancer
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