I haven't been able to successfully remove a potential threat Windows Defender has caught since I purchased my computer, now running Windows 8.1, two years ago. Every time I complete the scan and check Remove on the potential threats (Medium threat level), it gets to a certain point and just hangs. The program doesn't freeze but the green bar stops moving and it will not remove the threats. Trying to End Task warns me that doing so will make my system unstable, but I cannot close the the window because Apply Actions and Close are greyed out. In fact, the only way to shut the program down is to reboot entirely. I've let this run for hours on end with only two items to be removed, and as mentioned, this happens even after I reboot and try to run the scan again. It hangs during the removal process and never fixes the threats.
Is this a known issue with Windows Defender? As I said, it has been behaving this way since I purchased this PC in 2012. It runs the scan fine but it comes time for removal, the program hangs and will not stop hanging until I reboot. Windows Defender has never been able to delete a potential threat, and it's just lucky I've never had a serious one that I was concerned about removing immediately.