As "co.cc" increased its base of "customers", their reputation for providing free registration grew - and they became popular with scammers and spammers.
Last year, Google, weary of the overall poor search engine reputation of co.cc customers, de indexed all websites registered by co.cc. This week, co.cc apparently stopped serving DNS information for its "customer domains".
Strictly speaking, "co.cc" was not a registrar - and the blogs and websites published by its customers were not using registered domains.
The "Top Level domain co.cc" - which by its name implied an Internet service operating from the Cocos (Keeling) Islands - was in fact the domain "co", operating out of Korea, and registered in the Cocos (Keeling) Islands. All "domains" given out by "co.cc" were in fact sub domains to the domain co.cc - and this is where the problem started.
All blogs and websites, published to a "co.cc" subdomain, were aggregated by the search engines as the "co.cc" domain. As the number of co.cc registered scammy and spammy websites increased, their search engine reputation dropped. Non spammy blogs and websites either went out of business, or were transferred to legally registered domains, because of the low reputation and lower search engine originated traffic.
Finally, the owners of co.cc - supposedly "JONG SUNG, KIM" of "GOYANG,GYEOUNGGI" - realised that their run was over, and that they could no longer hide their scams and spams behind legitimate blogs and websites. Apparently, they have now shut their doors.
The old adage comes to mind.
You don't get something for nothing.
If you registered your custom domain using co.cc - and your blog is now offline - you're going to have to publish the blog back to BlogSpot, to get it online again. If you want to use a domain URL, you have to repeat the custom domain setup process - starting with a new, properly paid for, domain URL.
(Update 2015/02): We now have more of the same, from "co.vu".