The leak comes from Organization for Security and Cooperation in Europe (https://www.oscepa.org/) which pretty much explains itself in what it does.
The Parliamentary Assembly of the OSCE is the parliamentary dimension of the Organization for Security and Co-operation in Europe, whose 56 participating States span the geographical area from Vancouver to Vladivostok. The primary task of the 320 member Assembly is to facilitate inter-parliamentary dialogue, an important aspect of the overall effort to meet the challenges of democracy throughout the OSCE area.
The leaked data is a heap of PDF, docx, .msg and a dump of emails in a txt file.and also been tagged with the #5Nov tag on twitter making this one of the largest breaches for this operation so far. At time of publishing i have not had time to start going over all the information but will do shortly and hopefully can get some more information out of this. The first file i did view (0078_001.pdf) i caught notice of talks about honouring Nazis for the civilian killings, i may have this wrong but I'm sure this it not what a security organization is about. https://www.par-anoia.net/assessment/at/OSCE/