"co.tv" is not an official hierarchy; it is a domain (co.tv) owned by a company who offers free subdomain redirection services, like co.nr.
This company offers free co.tv subdomains. Due to the large use by website spammers of subdomains from co.tv in July 2011 Google removed .co.tv websites from its search results. This had no impact on other .tv websites.
According to Lucian Constantin at Softpedia, "CO.TV is a free domain provider that is obviously being abused by the people behind this campaign. All of the rogue domains used are hosted on the same IP address." Such unconventional usage of TLDs in domain names are sometimes known as domain hacks.
The company closed on the 31 October 2011. All existing domains were canceled.
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