Yes, we know. It's something to do with external content, most probably from AddThis. We've been trying to get to the bottom of this since Saturday, when Ex_Brit flagged it internally. There are threads about it (read the unfolding story) at
Site Advisor problem?
McAfee banner "We tested this page and blocked content...." even on community.mcafee.com
Why is my website getting a blocked message from Site Advisor?
Blog Getting Site Adviser Popup - AND Mcafees Site As Well??