"These files might be harmful to your computer."

In Windows 10, every time I try to drag-and-drop a file from a local directory into Box, I get a Windows Security pop-up that says “These files might be harmful to your computer” and “Your Internet security settings suggest that one or more files may be harmful. Do you want to use it anyway?”  I’ve messed around with the “Internet Properties” settings for an hour now and I can’t make this warning go away.