Unwanted mouse activity during mousedown on Windows 10

If this is not the appropriate community for this, let me know and move this. Starting a couple months ago, when I click left mouse button and hold it down, almost immediately extra activity takes place that interrupts my action. For example if I am highlighting a region in a spreadsheet. First thing I did was try a new mouse, but the unwanted activity continues. I've run virus scans, rootkit revealer, these come up clean. From what I barely remember about Windows API, something would have to be hooking into the events for mouse to receive messages, then running its own actions. How can I dete

Question by Robert Kerr on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.