Finding the same problem with one of my sites. Discovered after looking into why the feed wasn’t updating in Google Reader. It comes up on several scans, but I can’t seem to see it myself when looking at the source on the webpage, or looking in the index.php file (as someone in this thread did). I’ve reinstalled wordpress (the easy way through the updates menu), and it remains.
I’m running an Automattic theme (coraline) and only have three plugins running (Akismet, Jetpack by WordPress.com, and WP Super Cache), all extremely reputable.
I’ll post a link to the site if that’s deemed kosher. I have scanned my computer (running OS X 10.7) and it is clean.
What I don’t understand is how this code got on the website, and why I can’t see it.
Any help is very appreciated.
EDIT: Just discovered something. The code does not appear on the site when I am logged in. This explains why I was not able to see it in the source.