Detected: PUA:Win32/QBitTorrent
(not saying it is a virus or if the Windows Defender is doing a good or bad job, just letting you guys know this).
The detection is in qbittorrent_4.3.4.1_x64_setupexe->(UPX)->(nsis-6-e) and in qbittorrent.exe
(WDefender didn't blocked or complained about the setup, just blocked the execution... I guess all you need to do to create a virus that pass through WDefender is to make a setup.exe =P)
