yeah - that whole Karma thing. Plus you can be fairly confident that your library Overdrive Website isn't going to try and stick a virus on your computer.
As for as getting books from Overdrive for the Darknet, I don't know. My 2 Overdrive accounts (local and Singapore) don't usually get the "Bestsellers" until at minimum a week or two after release date. It is extremely rare anymore that they allow you to put in a hold for a book that is yet to be released. I suspect by the time Overdrive has the book available, it's likely already running free on the torrent sites.