smallish ads appear sneakily from bottom, going upward on my screen
You might be speaking of the sidebar ads, though that's not quite an accurate description. There are no ads that change position on their own. The ads will move only when you scroll the page, just like other content on the page does. However, most of the content on the page has static positioning, which means it can move off the screen if you scroll far enough away from it. But the sidebar ads have sticky positioning, which means they stop moving up once they reach the top of the screen.
You might be speaking of the sidebar ads, though that's not quite an accurate description. There are no ads that change position on their own. The ads will move only when you scroll the page, just like other content on the page does. However, most of the content on the page has static positioning, which means it can move off the screen if you scroll far enough away from it. But the sidebar ads have sticky positioning, which means they stop moving up once they reach the top of the screen.