Well done plaintiff
High time too
The European Court of Justice has been asked to rule on the issue of whether or not dynamic IP addresses constitute private data. The request comes from a national German court in relation to a case where the plaintiff claims that "storage of dynamic IP addresses" assigned to him breach his data protection rights. Under EU …
It's not just the ISP. It affects all service providers, especially aggregate ones like the advertisers, who can and do associate an IP address with a specific individual rather than using one-way hashes for the value of a session.
An ISP would have to demonstrate a legitimate business purpose for keeping historical data and to be honest one doesn't spring to mind, however most of this stuff is just captured automatically and nobody bothers to delete it. What the plaintiff should realise is while the court might rule that retention of this data by the ISP is a breach of privacy, if the relevant authorities believe that retaining this data is required for legitimate law enforcement purposes the data will simply be add to the relevant orders issued to ISPs and it would be retained that way