The plugin is a replacement for the standard VirtueMart search plugin, useful for the case when you want to make one of more of your categories not showing up on search. For example you want to show up your sold items in the site, for historical reference and/or SEO reasons, but don't want to show them up in the site search results.
The plugin has an extra field compared with the standard VirtueMart search plugin, where you can enter a comma delimited list of category ID's you want to exclude from search results.
Be sure to unpublish the Search - Virtuemart (or VirtueMart Product) search plugin, and publish instead this one, showing up in plugin list as
Search - VirtueMart Alternate search
Be aware, that if a product is shown in multiple categories then still might be found in one of categories belonging to is not on the blocking list!