I think the implication is that had they been built on an internally built OS(es) they would have not been open to infections already existent, not that Linux is more prone to infections than alternative OSes.
I have to say I have more of a problem with the advertising exchange that is allowing this to happen than the "adware" company itself. Rubicon has to not only represent the campaign buyers interests but also maintain publisher brand safety to sustain a business model. It's just a matter of time before real publishers will inevitably leave Rubicon if they continue to disregard this fact.
Every year there is some new gadget at CES that charges wirelessly in some new, innovative way, but is never heard from again. I guess I'll be a believer when I see it for the first time as a consumer somewhere.