http://www.caida.org/research/policy/country-level-ip-reputation/

We recently analyzed the reputation of a country's Internet (IPv4)
addresses by examining the number of blacklisted IPv4 addresses that
geolocate to a given country. We compared this indicator with two
qualitative measures of each country's governance. We hypothesized that
countries with more transparent, democratic governmental institutions
would harbor a smaller fraction of misbehaving (blacklisted) hosts. The
available data confirms this hypothesis. A similar correlation exists
between perceived corruption and fraction of blacklisted IP addresses.

NZ at the edge of the graph (CPI: very clean) but has a slightly higher
fraction of spamming hosts than Australia.