Sorry for the delayed response, in fact the version of Site Advisor what you get from Security Center (or) from www.siteadvisor.com are the same. But there is one other paid version which Site Advisor Plus.
Please refer to this link for more reference http://www.siteadvisor.com/download/windows.html
Thanks for the reply. The reason for asking was that McAfee Security Center came with my new Dell computer so, in about a year, I need to decide whether tor not to continue on a paid basis. If I don't it would be useful to know that the free version of Site Advisor is the same if I wished to continue using it.