Filters & Conditions are probably one of the most underutilized features in EnCase and they can certainly help with issues like this when you have already run a search and then later realized the keyword was not the best choice. The best way to avoid this is to think ahead and use a good keyword that eliminates a lot of the noise for you and will hopefully leave you with just relevant hits.
Lets first talk about some ideas when crafting your keyword(s) to save you time later. For the purposes of this article, lets assume I want to search for the ANSI keyword "soft". As you can image, this keyword is likely to return thousands and thousands of search hits that are not relevant and create a lot of noise that I would have to filter through to get to the good stuff.
Admittedly, most people could predict that a keyword of 'soft' would result in a lot of hits (software, Microsoft, etc). But sometimes its not that apparent until after you start the search and later realize that your unique keyword is not so unique after all. This is where we will leverage a condition to help, but lets get back to choosing a good keyword.
Int he past, I have seen a lot of examiners create a keyword such as " soft ". Yes, that's a space in front and a space after the keyword itself. While this may work for a small percentage of the hits, this will most definitely miss things you would probably want to see. I do not recommend you ever use a keyword like this except in very rare unique cases. While this keyword would certainly exclude hits such as "Microsoft" & "software", you are also going to miss "soft." or "soft" at the beginning of a line.
Using a test image, a search of " soft " (space before and after the keyword) results in 167 search hits being found.
Another approach is to use the "Whole Word" option in EnCase: