unsolicited app sites

twice this month while clicking on projects to open instructions, I had app sites with pornographic imagines pop-up. I've clicked back to exit and return to the main screen and just had more and more pop-up, I had to shut-down my computer and reboot. I don't know if others had had this happen. I've 58 years old, and I don't like it, I know it's don't intentional, but I don't stay on to see what the website is long enough to copy it so I can report it.