As is tradition, Release 274 is being flagged by Windows Defender as “Win32/Fuerboos.A!cl”. This is a generic heuristic detection, which means it’s being flagged because it “looks like” something that could potentially be malicious. This is of course a false-positive, and it will hopefully be cleared soon in one of the next definition updates. I’ve already submitted a report to Microsoft, so all we can do now is play the waiting game.
In the meantime, if you’re having trouble running the program, you can add HDoujin Downloader’s folder to your exclusions list. You can find instructions explaining how to do this here. If you had better luck with Release 273 and want to downgrade until Release 274 is whitelisted, you can also download the previous release here.
Since this happens every couple of releases and I’m always flooded with messages asking about it, I’ve made a FAQ page you can also check out with more information about why this happens and how to fix it.