Without question - India. This comes from personal experience.
It is not as much spam per se as it is link builders trying to hide links, drop names, have SEO friendly signatures, fake signatures with multiple links, etc. Essentially it is spam and usually when I notice this type of behavior - I delete it.
Without question, it's China. This also comes from personal experience. And this was pure spam - no attempt to be sly. Next up for pure spam is VietNam, then France and on a small scale, Russia.
The link builders come from all over, but mostly from India, Pakistan, UK and USA.
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