Annoying as the full screen ads are, so far I am sort of tolerating them since they are not trying to be anything else than (annoying) ads shown at my face.
But today they went to the next level so to speak, and I got the ad shown below.
I think these "your computer/phone/etc is infected, click HERE to fix it asap" type ads are one of the lowest ones, trying to scare people installing/downloading something they otherwise wouldn't do.
If Opera must shows ads to users, ignoring the built-in ads block settings, I hope they at least filter out the sleaziest ones.