.co.cc is a free domain service, which gives full DNS control. Why is it consider as spam?
You'll find the explanation in Wikipedia - http://en.wikipedia.org/wiki/.cc - co.cc is a domain owned by a company which sells subdomains for redirection, and most of them are used by spammers.
This one can be tracked back to the fact that these domains are free. They're not very popular at all beyond the free aspect. A lot of spammers will use these domains because of this. With the low popularity of the domain extension, a lot of places consider co.cc to be the domain, and the actual domain to be a sub-domain, which means "abc.co.cc" is considered to be the same as "xyz.co.cc". This is why I changed my site over to a new domain.