There's no surprise to be had with Sandvine's latest research, which finds that Internet viruses could be costing ISPs up to $370m worldwide in 2004. The study found that, on any given day, roughly 5% of an ISP's home user base will be infected by some kind of worm:

Most ISP networks contain varying degrees of latent worm activity and experience daily denial of service (DoS) attacks, the study found. Traffic generated by the six-month old Nachi worm and Trojan infections created the biggest problems.

On any given day, between two and 12 per cent of all Internet traffic moving across ISP networks is malicious. Even on well-run networks with dedicated security departments, malicious traffic makes an average of five per cent of all data.

This adds up to millions of dollars of expenditure in needless transit fees ($60,000 a year for a typical 100K-subscriber service provider, Sandvine estimates) and increased customer support charges.

Unsecured broadband users take the brunt of blame for allowing their systems to remain vulnerable and exasperate any problems.

In the meantime ISPs are finding their costs go up as they try to cope with rising broadband use, anti-virus solutions and spam filtering. Some of this filters down to customers, while others absorb the costs internally - for now.

Either way, anybody connecting to the Internet without a form of anti-virus checking software installed (one that includes e-mail scanning) is hurting everybody. More @ The Register.