SPAMfighter do not work by looking for specific words in emails because this is not a very effective way of filtering spam.
A word which is often seen in spam mails is "Viagra". But even if we start filtering for this specific word it would not help much as spammers unfortunately are not that stupid that they write it exactly like that in their emails. As long as what the spammers write is perceived by the human brain as "Viagra" they are satisfied as their message is delivered. The word "Viagra" can be spelled and misspelled in more then 100,000 ways which all will be instantly recognized as "Viagra" even if it is not exactly what it says, because just an extra space in the word would mean that it would be something completely different that should be looked for - just as if you were to take your own name and put in an additional space then it would no longer be your name.
This would mean that the time it would take to scan an email would increase tremendously, because the 100,000 variations of "Viagra" is only the tip of the iceberg. There are also words such as "Casino", "Sex" etc, and even it just takes a fraction of a second pr word, and the variations of these, which the mails have to be looked through for, then it will accumulate.
So the practice of searching for specific words would mean that there would come a point where it would take more time to filter the mails then it would to manually discard the spam mails, and this would completely undermine the idea of using a spamfilter since no one would be interested in having to wait several minutes for a single email merely because it has to go through a spamfilter.
