A Russian-linked group of hackers, who recently attacked government websites, stole documents, among which were those that related to Ukraine. This is reported with reference to its own sources by the German Der Spiegel.
In particular, among the six files that were stolen, there were documents that related to negotiations between Britain and the EU regarding Brexit, as well as EU negotiations with Ukraine and Belarus.
At the same time, it is stressed that the leakage of documents concerning Ukraine and Belarus was controlled: it happened already after the security service learned about the cyberattack.