Though the U.S. remains the world's worst source of spam, South Korea and China are quickly catching up as anti-spam efforts lower the amount of spam emanating from the U.S., reports CNET, citing a report from security software maker Sophos. According to data from April to September, the U.S. was the point of origin for about 26 percent of global spam, down from nearly 42 percent a year ago. Spam from South Korea and China increased nearly 20 percent and 16 percent, respectively, from 12 percent and 9 percent.

Sophos attributes the decline in U.S. spam in part to a crackdown against fraudulent email, including the imposition of jail sentences for spammers, tighter legislation and better system security. The threat of legal punishment has also worked in Canada, Sophos said, noting that spam generation there had fallen to 2.5 percent from more than 7 percent last year.

More than 60 percent of spam messages are generated by zombie computers, made so via the use of viruses or other malicious code, allowing the culprits to be in one country to exploit computers in another, Sophos said.