My computer was invaded today!
Last night, I shut down my computer properly for sure. I didn't experience any abnormal computer issue at all. This afternoon, when I came back home from work, and turned on my computer, the display setting was changed to bigger fond. The whole desktop was distorted because the large font size.
The desktop display won't change by itself. Someone must have entered my home without my knowledge, and hacked into my computer and did all this.