A report from Symantec, the online security firm, alleges that the RBN has links with the criminal underground and government in Russia.
However, in recent days huge numbers of RBN-hosted sites have disappeared from the Web, leading analysts to speculate that the group is revamping its business model.
"RBN is reorganizing," said Raimund Genes, the chief technology officer of Trend Micro, a security group that has traced attacks by the RBN on corporate and government sites across Europe and US back to servers based in Panama.
One reason is thought to be the recent threats by Russian authorities to impose tougher penalties on Internet criminals.
Another was that large legitimate Internet service providers — which the RBN relies on to provide it with Internet access — have dropped it as a customer as its activities became more and more notorious