I have tried using Shareaza and found that it took over my torrent file handling and magnet links even though I told it not to at install, and then turned that off in the setting afterwards. In fact, it took them over so well, qBitTorrent can't even take them back any more. So I uninstalled Shareaza and found that whatever it did to my registry survived after uninstall, so I opened up my registry editor (remember this is after uninstallation) and found literally dozens of Shareaza entries all over, from the magnet handler to media handlers. There may have been hundreds, I stopped deleting them after I hit 20 or so and am now about to use system restore to fix this. For a program that says it intends to play nice with a user's computer, it certainly doesn't play very nice.
Having to use system restore to clean up after the mess Shareaza made to my computer is serious. And I am quite unimpressed.