If you wonder how it works, it is simple. The actual website security rankings are expressed by three colors: green for safe websites, yellow for minor risk issues, red for serious risk issues like websites that install viruses/trojans on your computer and the gray color is for websites that have not been tested by McAfee yet.
The developer underlines that SiteAdvisor works with most search engines. When the user searches for something on the internet using a search engine, at the right end of all the results are the indicators (red, yellow, green or gray) that label all the search results. When placing the mouse pointer on the indicator, no matter the color, a bubble appears that offers more information and options about that website.