From Wikipedia:
"Suggestions the co.cc site pops up for free domain names to register include "bestantivir" and "autoloan," belying its true use - the creation of spam domains. Step-by-step instructions for spammers to use free hosting services like Blogger, Windows Live, and Google Apps for Nonprofits are included on its homepage, under the heading "Mapping with co.cc".
Due to the large use by website spammers of subdomains from co.cc, in July 2011 Google removed the over 11 million .co.cc websites from its search results. This had no impact on other .cc websites"