The computer giant 's Global Business Security Index for the first half of 2005 shows that the ratio of spam to wanted, legitimate email has decreased from 83% in January to 67% in June.
However, the report reveals that customised attacks to gain cash out of firms, including data-extracting viruses are increasing.
Virus-laden email increased by a massive 50% during the first half of 2005 and there were an estimated 237m security attacks during the same period.
Governments around the world are the most targeted, with 54m attacks, while manufacturing ranked second, with 36m online assaults.
It is not simply the number of the emails, but their malicious nature that is a problem as well, with as many as one in 28 emails carrying a virus in June, the report found.
IBM is particularly concerned about the rise of phishing attacks, linked to money laundering and identity fraud and so called "spear fishing", which is a highly targeted attack to extract data.
John Lutz, IBM financial services sector general manager, said: "IBM advises its clients to rapidly adopt a holistic, enterprise-wide approach to security and risk management."
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