This is fascinating research about how the underlying training data for a machine-learning system can be inadvertently exposed. Basically, if a machine-learning system trains on a dataset that contains secret information, in some cases an attacker can query the system to extract that secret information. My guess is that there is a lot more research to be done here.
EDITED TO ADD (3/9): Some interesting links on the subject.
*** This is a Security Bloggers Network syndicated blog from Schneier on Security authored by Bruce Schneier. Read the original post at: https://www.schneier.com/blog/archives/2018/03/extracting_secr.html