The survey found that 50% of spam, or unsolicited mail was confined to only 20 ISPs, the BBC reported.
The large scale survey was done by Giovane Cesar Moreira Moura who found that some internet areas represented a particular risk for users as sources of malicious mail.
India, Vietnam and Brazil were singled out as dangerous areas for spam, but unmatched by Spectranet in Nigeria.
Around 62% of the addresses controlled by that ISP were found to be sending spam.
The study, which examined 42 201 ISPs, did not imply that the network was a direct indicator of the source of spam as cyber criminals can route malicious mail through compromised computers and even company networks.
Spam was on a declining trend at the end of 2012, a security company said.
"In the last month, we saw a further reduction in the amount of spam found in e-mail traffic - its share was down 3.4 percentage points, and fell to its lowest point since the start of the year - 73.8%," Kaspersky Lab told News24 last year.
Cyber criminals generally shift their methods of attack to platforms that become more popular with users.
In that sense, social networks are becoming targets of criminals, especially as the apparent social connections between users could lead to the theft of personal information.
"Social networks are not immune to spamming tactics; you see it also on forums on the internet. People are discussing a certain topic and suddenly there's a completely unrelated comment with an advert," managing director of BulkSMS.com Dr Pieter Streicher recently told News24.
Spam remains that most pressing concern of PC with about 68% more concerned about unsolicited mail that PC virus infection, a survey conducted by O+K Research found.
According to Technology Banker, cyber crime in SA cost R2.65bn, but 75% was recovered, bringing losses in 2012 to R662.5m.