Just kidding, the web server indeed was defaced by some script kiddies through an apparent vulnerability in the server management software, still checking.
I'm removing your screenshot, no need to give these criminals more publicity, that's mainly what they are after.
I was trying this site this morning and my anti virus stopped access because of a Trojan virus on the home page. I am trying a new anti virus program so I don't know if it was being hyper sensitive or not but the fact that your server was hacked makes me think maybe it was a valid catch.
It's not alerting you now though right? The index.php that the hacker inserted did have a small javascript, so maybe that was the cause. Although I didn't notice any alerts (or heard of any) on any of the hacked sites.