The co.cc URL has been known to host spammers, who create spam blogs, or "splogs", often with nonsense names. Due to such spamming, in July 2011 Google removed over 11 million .co.cc websites from its search results. Legitimate sites (per Google's Webmaster Guidelines) on the .co.cc subdomain could send a reconsideration request to Google to have their specific site excluded from the ban.
