Half of all junk mail, phishing attacks and other malicious messages emerge from just 20 ISPs.
Internet service providers (ISP) are mainly responsible for majority of internet threats such as spam and phishing, according to a new study.
The survey carried out by Giovane Cesar Moreira Moura involved more than 42,000 ISPs and reported that about 50% of all junk mail on the net came from just 20 ISPs.
According to the study, some networks could be classified into 'bad neighbourhoods' as they were the main sources of spreading malicious activity.
Many of the accused networks were from India, Vietnam and Brazil, while Nigeria's Spectranet was claimed to be Internet's most crime-ridden network, with 62% of all the addresses controlled by ISPs were responsible for sending out spam.
According to Moura, the study was aimed at computer security tools that examine the net addresses of email and other messages to assist in working out if they were junk or legal.
"If network security engineers want to reduce the incidence of attacks on the Internet, they should start by tackling networks where attacks are more frequently originated," Moura said.
The networks involved in malicious activity also tended to focus on a particular malicious message or attack, the study said.
Additionally, cyber criminals route spam and other traffic through hijacked PCs or pass it across compromised corporate networks that connect the internet via an ISP, the study revealed.