Six months ago, Google publicly wiped out any co.cc domain from showing in Google's search results. That subdomain wide penalty seems to have now beenlifted.
A search for [site:co.cc] returns over a 100 million results now:
The results started appearing about ten days ago, when before, it returned nothing:
I am not sure if Google changed their mind of this penalty was automatically lifted after a certain time period? Who knows if the subdomain will be banned again when Googlers return from their holiday break.
But at least now you can check to see just how spammy the co.cc sites are.
Forum discussion at Google Webmaster Help.
