Sixty-five per cent of all emails sent in June 2004 were spam - up from just eight per cent three years ago, according to email monitoring company Brightmail.
The steady increase in spam rates shows no sign of slowing, and existing legislation such as the US Can Spam Act will have little effect, claimed the company.
"People are underestimating the spammers," said Enrique Salem, senior vice president of gateway solutions at Brightmail.
"These figures are dramatic. In many ways it's almost a denial of service attack on the email infrastructure. There's a fundamental flaw in the infrastructure: when email was designed we weren't thinking about spam or phishing."
The latest figures also show that non-English language spam is beginning to grow. Sixteen per cent of spam is now in languages other than English, reflecting the increasingly international nature of web traffic.
Brightmail also warned that the rise of phishing attacks is not only having drastic financial effects on those caught out, but may be harming public confidence in the safety and credibility of internet business.
The company called for a public education campaign by government and industry to teach users how to surf the internet safely.
Research by content security company Clearswift earlier this month found that financial and pharmaceutical spam was the fastest growing, and now makes up 69.6 per cent of spam.
But Clearswift also warned that spam is increasingly being used as a vehicle for financial scams, such as phishing.
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