The United States and China remained atop the list of countries spewing spam for the third quarter, U.K.-based security vendor Sophos said Monday, and the former had the dubious honor of extending its lead in the battle for spam share.

According to Sophos, servers in the U.S. sent 21.6% of the world's spam during the August-September time frame. China, in second, accounted for 13.4%. France, South Korea, and Spain rounded out the top five. China's share was nearly 7% off the previous quarter, while the U.S.'s part declined by 1.6%.

As recently as April, Sophos predicted that China would steal the spam crown from the U.S.

Sophos attributed the widening lead of the U.S. in spam sending during the quarter to the widely spread Stration worm (aka Warezov). "The steady increase in the volume of spam seen traveling across the net is directly related to the enormous rise in Stration worm strains in recent months," said Ron O'Brien, Sophos senior security analyst, in a statement. Stration arrives with an English-only message, and hijacks compromised machines to use as spam "zombies."

When spam origins are grouped by continent, not country, Asia comes out on top, with 34.1%. Europe and North America follow with 31.9% and 24.2%, respectively. The ranking for the third quarter were identical to the previous three-month period, said Sophos, although Asia's share fell, Europe's climbed, and North America's remained flat.