Several WordPress versions ago, I downloaded a three-column theme called "Royaline" from WordPress.org and used it on my site, LitKicks.com. After almost a year with this theme, LitKicks was suddenly blocked from Google due to a prescription drug spam that turned out (I finally discovered after much work) was embedded in the theme. It can be found in defaultFilters.php in wp-includes, and it is triggered a footer do_action. The spam links only show up in requests that contain identifiers for search engine bots, so you won't see the links when you view source. Anybody who is using the Royaline theme should be aware that you may be blocked from Google. This theme should not be used, but if you already use it you can disable the spam by removing the footer do_action (and, to be safe, remove the function from defaultFilters.php as well).