Things like this make me fear banner ads mining bitcoins (not that they aren't already).
Nitpick: Bitcoins can't effectively be mined on anything but specialized ASIC hardware. Not even high-end GPUs. They could theoretically mine other cryptocurrencies, though.
Nitpick of your nitpick: GPU and even CPU can mine Bitcoin. It's considered ineffective because of the power consumption and hardware time relative to the value (and compared to what custom ASICs can do once you've made that investment) makes it prohibitively expensive for the returns one gets. If it was being mined on other people's power and time it's more effective than not mining at all and you'd not be paying for the power or hardware time. Etherium or Litecoin would be more effectively mined that way than Bitcoin, but anything you're getting for free is free. Of course the ethical and moral implications here are very negative.