While the United States continues to be the world's worst source of spam, computers there are relaying <A HREF="http://news.zdnet.com/2100-1009_22-5894104.html?tag=zdnn.alert">far fewer junk emails</A> than a year ago, according to Sophos. In contrast, the spam volume from South Korea and China is substantially up, compared with the same period last year, the security software maker said in a report released Wednesday. The report covered Sophos' analysis of messages received in its scanning network between April and September this year.