Hello Bsmith583, indeed the Blizzard launcher does seem to be a legitimate program for downloading games such as World of Warcraft and your Diablo III game. What you can do is use Immunet's "Restore" feature. When a file or files are restored from Quarantine they are automatically moved to the Exclusion list and will no longer be scanned. It is very important, however, that only files you are "absolutely sure" are not malicious are restored from Quarantine or you could be unleashing malware into your system. Just wanted to mention that once again as a precaution. Not a bad idea to check to make sure the downloader hasn't been compromised in some way before you use the Blizzard launcher & install your game such as checking it with VirusTotal's database and/or on-line scanner or use some other on-line virus scanner first. Of course this is after Immunet quits quarantining the launcher. Always better being safe than sorry!
How you restore a file is first click on the Immunet icon to launch the GUI > click on the word Quarantine located just below the History tab > click on the file(s) in question and choose the "Restore" option. Like I mentioned before this will move the file(s) to the Exclusion list in the Settings.
If that doesn't work another option would be to completely kill Immunet before trying to download the game. If you're fimiliar with CMD commands you can try this.
Right click on the Immunet sys tray icon and choose Hide Tray Icon from the little context menu or use Task Manager (press Ctrl, Alt, Delete at the same time) to manually kill iptray.exe > click on Start > type cmd in the search bar above the Start button and click on the little CMD icon when it populates, this will launch a small CMD window > type exactly: net stop immunetprotect > press Enter and wait a few seconds until it says the Immunet service has stopped, this will kill sfc.exe, Immunet's main process > close the CMD window & then download & install your game. Then just reboot or to launch Immunet again without rebooting, open another CMD window and type exactly: net start immunetprotect > press Enter and wait a few seconds until it says that the Immunet service has started, this will relaunch sfc.exe > close the CMD window & then click on the Desktop or the icon located in Immunet's All Programs folder to relaunch the Graphic User Interface process, iptray.exe.
I hope this info helps and if you continue to have problems with Immunet regarding this issue feel free to add another thread to this topic.
Best wishes, Ritchie...