According to research from network analysis and filtering firm Sandvine, the high cost is because of the increase in worm attacks and the growing number of consumers moving to broadband.
A spokesman for the company said that $370 million includes responsive action to support infected customers, transit costs of additional internet traffic and the damage to reputation worms can cause.
The firm also said the problem is not restricted to any particular size of ISP, and that support issues account for more than three quarters of the total cost of the problem.
