I have accidentally come across in a Google Groups thread which has a response from Matt Cutts of Google explaining their was a bug in Google's algorithm for detecting content spam due to an IFrame. There was a discussion regarding censorship asked by a member in the Google Webmaster forum and it goes like this
DId google censor atlasshrugs.com content? I get no hits of articles
on this site.
for which Matt replies in this way
"Hi, we looked into this, and the blog in question was ranking lower in
our search results because of an algorithmic error that has now been
fixed; the site's drop in our search results had nothing to do with
the views expressed on the site. Essentially, our search algorithm saw
a large area on the blog that was due to an IFRAME included from
another site and that looked spammy to our automatic classifier. I
believe that this bug has been fixed now. We also added additional
safety checks to the relevant system that would escalate to an
engineer if this site had the same issue in the future.
The site should be ranking higher in Google within 24 hours according
to the people that I talked to. Thanks for mentioning the site on this
discussion group to give us feedback--I appreciate it.
Google Software Engineer "
SRobert, we adjusted the algorithm in question to make more robust, so
the change also benefits any other sites there were affected.
Its very rare we often find Matt replying to someone in the forum and this has caught my attention. From the above explanation you could see that Matt saying that Google had an "algorithmic error" because of an "IFRAME" included from another site which looked as spam to its "automatic classifier".
More information can be found in the Google Groups