Another article on the prospect that SoBig is being created as a money-making scheme: New York Times: Spam-for-Money Plan Suspected by Expert on E-Mail Viruses”
Still, there is no evidence given as to why they think this is commercial in nature. The closest the article comes is:
“There is some evidence that he’s been tied in with spammers,” said Bruce Hughes, director of malicious code research at Trusecure. Although many companies blacklist Internet addresses that are the sources of spam, a strategy that used computers commandeered by the SoBig program would be almost impossible to defeat.”
Of course “impossible to defeat” is hogwash. Blacklisting would be useless in this case (which might be a good thing since it is largely a failed strategy towards stemming the flow of unwanted messages), but Bayesian mail filters like Cloudmark or SpamBayes would have no trouble with this.