Your site doesn't work for me...
But I doubt a "hacker" is going to waste their time make your site go grey now, what would be the point in that?
Its a default feature of vBulletin, it turns the site grey when you select the button to logout and the pop-up appears to confirm your action. Try reverting the template you have been editing (save a copy in notepad or something if you need to), and see if your issue goes away.