According to The Register, the .co.cc subdomain, owned independently by a Korean company, is not an authorized second-level domain (such as .co.uk). Google classified it as a “freehost,” meaning that it allows users to register single sites for free.
Oliver Fisher, a member of the Google Anti-Malware Team, wrote a post on the search engine’s Online Security Blog to explain the massive take-down.
“Google’s automated malware scanning systems detect sites that distribute malware,” said Fisher. “To help protect users we recently modified those systems to identify bulk subdomain services which are being abused. In some severe cases our systems may now flag the whole bulk domain.”
The Register notes that a recent report showed that .cc had twice as many phishing attacks as any other domain extension, especially because of the .co.cc subdomain. The company that owns .co.cc says it has 11,383,746 registered domains.
As Search Engine Land points out, Google wiped out content from a freehost before. For example, the search engine banned a Polish freehost due to a large volume of spam.
Google’s been vigilant about cutting down on spam since its early days, when employees had to manually search for porn sites to filter them out of results. Recently, the site introduced a series of changes to further cut down on spam and content farms.