Google released some statistics that reveal the top 10 malware sites in the world according to their site scanning research.
The data reveals that over 4000 sites are "set up for distributing malware by massively compromising popular web sites." Of all those sites, over 1400 of them are hosted in top-level domain .cn, which belongs to China.
Six of the top 10 use .cn domain names and all 10 are responsible for compromising at least 10,000 Web site - some were responsible for compromising more than 60,000 Web sites.
You might want to have a look at the report and blacklist all of the 10 top