Dutch market research group Blauw has gone to court in an effort to find out more about last week’s massive data leak, which appears to stem from market research software created by Dutch company Nebu.

Blauw wants Nebu to come clean about how much and what data has been leaked and how it could happen, but Nebu has, the company claims, been short on details. Blauw is required by law to inform its clients about the leak.

VodafoneZiggo, the NS and health insurance company CZ are among the companies whose client data appears to have been downloaded.

‘We still don’t know if personal information has leaked out,’ Blauw director Jos Vink told Nu.nl. ‘At the end of March our software supplier Nebu reported a data leak. We have asked what data and how it could happen but we have not had any answers.’

Tuesday’s court case was aimed at making Nebu, which is part of Canadian stock exchange listed company Enghouse, provide more details about the leak. According to its website, Nebu provides software to market research companies in several other European countries.

Nebu’s lawyer told the court hearing on Tuesday that communication about the leak had ‘not gone well’ at the beginning.

‘The cyber incident is Nebu’s main priority at the moment,’ the lawyer is quoted as saying by the Volkskrant. ‘But if things are not clear for Nebu, it cannot extend the necessary information.’

The court will give its verdict on Thursday.