I figured it out. I had an old, outdated version of an antivirus program that I thought was no longer running. It was no longer running virus protection, but it was continuing to create log files. It had accelerated the logging and it was running new log files every minute. I deleted the old antivirus program, opened the hidden folders in Windows, and found the log folder. It was an 854 GB folder, full of nothing but log files for an antivirus program that was offering no protection to my machine. It is deleted now. It quickly filled up a 919 GB partition on a 1TB HDD. I heard long ago that if you have a problem that looks like a virus, but isn't, the problem is very likely to be the antivirus. Lesson learned.