The article argues that the US is #1 because of "the deeply insecure state of American computing". But that doesn't make sense. It's arguable that pirated versions of Windows are less secure, because they may contain botnet clients and other malware. And it's my impression that pirated versions of Windows are less common in the US than in other countries. If NBER would accept my 2 USD in Bitcoins, I could get some facts from Susan Athey and Scott Stern (December 2013) The Nature and Incidence of Software Piracy: Evidence from Windows < http://www.nber.org/papers/w19755 >. But they don't Anyway, maybe the US is #1 for botnet slaves because countries like China and Russia tend to tolerate botnet herders as long as they don't target locals
Just because the spam comes from Spain it doesn't mean it's generated by Spanish individuals. I might upset people, but with the spam numbers you can make an idea about the literacy of a population in computer matters.