1) The sites are re-scanned about ONCE A YEAR. That's not joke, see
citing:

“– How long does this re-assessment period last?
–The re-assessment period can vary from as few as 10 calendar days to as many as 365 calendar days.”

Is it good for a real security? The URLs and files on a modern websites are updated very often, so scanning a website once a year is a completely useless and even dangerous and malicious practice, because it may damage website's ownders business and ruine his reputation. Of course, MCAfee doesn't care. Why? I'll explaint that later.

2) MCafee siteadvisor is based on a reputation system, where users are posting their comments with a site rating. That's a great chance for a competition to publish a black PR feedback and reduce a competing site rating. And actually most users posting the comments there are mcafee bots, which are given the most rating 9/9, so you cannot dispute their posts! What a crap, a machine revolution??

3) MCAfee is interested to assign a bad rating to a website. First, more red sites – more scares, and the user see how the software is useful to protect him, even an innocent website is blocked. The most important part of that is MCAFEE EARNS NONEY on SiteAdvisor, although the end-user software is free. How? That's simple- if you don't want to see your site blocked by SiteAdvisor, you can PAY to mcafee to have a green rating “Tested daily by MCAfee”. That green rating means nothing for the end-user, because I personally saw that http://www.refog.com website containing a commercial spy software had a green “Tested by MCAfee” rating for years.

so, MCafee is interested to put a red rating on your website! Actually, one of my websites also has a red rating , and while trying to find out why, I see that the files listed as a “viruses” don't even exist on my website, and the date is from Sep 2009 , more than 6 months ago!! Also some of definitely innocent downloads are listed as torjans and viruses! OK, I've contacted their support, they even replied me the next day, but NOTHING was done, now a month after my request! I also saw that well-known websites like http://www.snapfiles.com were suffering because of MCAfee blocking.
There was also a story in some blog, that a website owner stopped to pay to MCafee for a green rating, and after some time his rating was changed to yellow for no real reason! so they offer “not forget to pay them”!

A great advice – stay away from this “security” business, the main purpose of which is to steal your money. There are enough free solutions available like Microsoft Security Essentials, AVG, AVast, Avira etc. Not all of them are great, but at least they are free. And actually the chance of being infected with sometihng is low if you learn some basic rules of surfing the web!