Several readers have contacted IDGNet to confirm they too have had problems with excessive charges on their JetStream accounts.
Antony Stening, spokesman for Venture Taranaki, the region's development agency, is waiting for this month's bill after spending the first week of the month frantically fending off email from infected sources in France and Australia.
"They were infected with Sircam and we were getting emails with about 200KB pouring in every couple of minutes."
For days his JetStream 600 account was receiving about 500MB a day.
"We contacted the help desk and I really felt quite powerless." After the usual wait on hold, Stening was told there was nothing Xtra could do to block the incoming email, even though he had the IP addresses.
"They said there was no way they could put any block in and there was nothing we could do about these emails and we would be billed for it at the end of the month."
In the end, Stening says they blocked the whole domain, which has lead to other problems. "Particularly with the Australian one because we do business with them, but we couldn't avoid it."
Being a development agency, Stening says Venture Taranaki relies on its communication systems to make money.
"Our trade is in information and we send and receive quite large files. For the rest of the month I know we've already reached our maximum and everything since we're paying for."
Stening says Venture Taranaki is a small agency of only 15 people and doesn't have its own staff.
"We had to call in Computerland to filter those addresses out and that's going to be another bill."
Stening says Venture Taranaki uses a Nokia M1122 modem that has its own firewall built in and runs another firewall, BorderManager, behind that.
Telecom spokesman Andrew Bristol says he cannot comment on individual issues but urges all Telecom JetStream users to contact Telecom if they have a problem with the service.
"We have a phone number for customers to contact us on if they do have problems 0800 253 878 and an email address email@example.com. We prefer email as we can respond quicker to that," says Bristol. He insists that users who install a firewall will be protected from DoS attacks and the costs they incur.
"It's my understanding that if you either install a firewall or unplug the modem when you're not using the connection you'll be safe."
Stening says it is ludicrous to expect users with an "always-on" connection to unplug their modems when not in use.
"We bought the service in part because it's always on. That's one of the selling points."
JetStream users can monitor their download amounts online. Another user who contacted IDGNet had printed off his monthly report with only a few days left to go in the month.
"I'd used about 600MB so I was quite surprised when the bill came in with over 4GB of data on it." He says he argued the case with Telecom who insisted he'd downloaded the additional data in the last week of the month.
"I asked them to show me how I'd done that because that would mean downloading at a faster rate than my modem can handle." Telecom eventually dropped the charges from his account.