Business users have suffered intermittent e-mail and Internet services for more than a week. Demon's helpline blamed "routing problems". One business user said, "It is getting worse and Demon's maintenance seems to be making no difference."
Another said, "We are able to work at only 25% capacity. What concerns me is that the time being taken to fix this is more characteristic of a small business which makes me lack confidence in Demon's ability to provide a service in future."
According to Demon - which has about 80,000 business customers - spammers have exploited wrongly-configured customer mail servers. Steve Kennedy, head of technology futures at Demon, said customers using always-on Internet have been targeted using probe software.
Spammers then injected massive volumes of spam onto the public Internet through Demon users with an open mail relay e-mail server configuration. This allows the server to accept mail from an external address and send it on to other external addresses.
Kennedy said, "There is no valid reason for any customer to be set to open mail relay. We will be proactively scanning for them and shutting those customers down. We are also implementing extra hardware to cope with the volume of bandwidth that is being eaten up."
Michael Halama, an analyst at Gartner, said, "Customers expect their Internet service provider to protect them from such things, even if it is the fault of other customers. It is no good for an ISP to not take some of the blame. Customers need to think carefully about moving to another supplier, given the mission-critical nature of e-mail and the general instability of the ISP sector."