Where in the world do most spam email messages come from?

According to a recent study by Sophos for July to September 2012 the top 3 countries and continents were:

By Country:

1. India: 16.1%  
2. Italy: 9.4%
3. USA: 6.5%

By Continent:

1. Asia: 48.7%
2. Europe: 28.2%
3. South America: 10.2%

Read more: India spews more spam than ever before, report finds