Spam Report Card 2004 - TechUpdate - ZDNet:
"More than 50 percent of e-mail is spam. Billions of spam attacks are launched each month. Spam costs U.S. companies at least $1 billion per year in security and human resources expenditures, as well as lost productivity. Increasingly, virus-infected machines are used to distribute spam and perpetuate additional fraud, such as phishing. Is combating spam a losing battle?"

http://techupdate.zdnet.com/special_report/Spam_Report_Card_2004.html