Click farms.
These are places, mostly in Asia, where workers "work" on hundreds of cell phones at the same time for a pittance.
Their boss is a click farmer or click farm master.
The employees run videos on the target websites, sign up for newsletters and distribute likes.
They create fake traffic on websites, so to speak.
Customers of these websites then believe that their advertising is well placed there.
You can hardly notice the fraud, because the click farm workers seem to behave like normal users.