Belgacom, which owns Skynet, has until 30 November to increase its download limits, the hacker’s message said, or the other account details will be made public. Until that date, 1,000 clients will have their details revealed.

A spokesman for Belgacom initially said there was no indication that the hacker is in possession of the information he claims to have. However, it later became clear that the 30 already posted are all genuine.

The hacker claims to be an American and says he is disgusted with Belgacom’s limit of 25 gigabytes of download capacity each month for normal internet clients. Download limits are only making their first appearance in the US, but here they have historically been much lower than they are now. Belgacom is not alone: Telenet, the other major ISP, allows 20 gigabytes. However, that is enough for all but the most avid downloader of videos or films: most people come nowhere close to using their limits in a month. Belgacom explained that its extra download packets, where users pay €5 for an additional 5Gb of capacity, sell only a few thousand a year.

The case is now being investigated by the federal police’s computer crime unit. Belgacom stressed that logins and passwords can be changed with little difficulty and that anyone who comes by that information illicitly will not be able to obtain, for example, access to online bank accounts or credit card details.