I read same allegation last week of exchanges indulging this sharp practice, especially on Bitcoin and then using clients funds to trade. No exchange was mentioned. As it was a sweeping allegation, I quickly made a rush to certain exchanges I use but couldn't find anything untoward. I don't know how this crazy things happen and I think names and link evidences (I mean concrete evidence, not social media link.) should be made available to the reading public so that we know these bad eggs.