I don't know exactly how anyone could measure that but there is one thing I know for sure and that goes back to the days when there was a serious alliance between porn sites and warez sites; for a significant period this was one of the major forces pushing the need for bigger bandwidth.

As long as people insist on having illegal software, there will be a huge surface attack.

Porn? Well, apparently there is a big demand, the .xxx domain will be in place very soon, with or without viruses.