Whether you use a blacklist or a whitelist... I think you must create the one which is smallest and/or with the least impact. I think a blacklist would be smaller, if you allow no words smaller than 4 characters to be used anyway.
You could add tagging to a response. So for example in your example the response is tagged with 'server' and 'down'. It would be possible to create a search on the tags.
pritaeas
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