From BBC News (link):
Statistics from security firm Sophos show that China is fast catching up the US as a source of junk e-mail.
According to Sophos, 23.1% of spam comes from computers in the US and 21.9% comes from China. The UK is tenth on the list of spam sources.
As a continent, Asia is the biggest source with 42.8% of unwanted commercial e-mail coming from that region.
See also “U.S. Sends Most Spam, China Hosts Most Spammer Sites” on TechWeb.com