I wasn't following the other thread, but I'm guessing your talking about either virus' or spyware. If virus, there are no "free" options that I know about. Trust in only the known virus software vendors - McAfee, Norton, etc.
If spyware, there are a few free options. One is called "Spybot". I've used it for years. I know of a few corporations that use it and corporations as a general rules of thumb are VERY leary of ALL downloadable software.
Sue