How much do worms and virus cost ISPs?

Of course, I'm certain Sandvine is selling something to solve the
problem, but it is still a very nice article with some measurable

"On any given day," its white paper concluded, "between 2 and 12 per cent
of all Internet traffic moving across service provider networks is
malicious. Even on well-run networks with dedicated security departments,
malicious traffic constitutes, on average, 5 per cent of all data

Service provider with about 100,000 subscribers will lose almost $60,000
in avoidable fees. A provider with one million subscribers will pay an
additional $350,000.