This is only one brand of spyware – there are many many out there.
In this case they put pop-ups or pop-unders on your site. Either they cover your site and induce your visitor to click on their ad, or they hover underneath, and if your visitor clicks on one of your links he thinks he has ended up at the place that uses the thiefware and plays there.
There are other programs that for instance underline certain words on your site – like Blackjack or slots or whatever – and if your visitor clicks he ends up at the thiefware casino.
All the casinos listed are using spyware. There are a lot more, too, and some affiliates use it also.
With some of these programs it is possible to submit sites you don’t want to steal from – and there is no excuse for our affiliate programs to allow theft from affiliates.