Adwarekiller gave a good answer, and I'll add some of my own notes.
* Distribution is mostly consolidating. A lot of adware companies used to both buy their own distribution through either pay per install or revenue share agreements and then monetize those users themselves. Now, the ecosystem is fracturing into companies that actually perform the distribution and companies that monetize those users.
* Large distribution companies: - IronSource (this article) - InstallMonetizer (YC funded as adwarekiller mentioned) - Web Pick Internet Holdings (InstallRex as adwarekiller referenced them) http://www.web-pick.com/ - Cross Rider https://crossrider.com/ - Ad Peak http://adpeak.com/ - Conduit & Perion http://conduit.com/ & http://www.perion.com/
* Large monetization companies: - Future Ads & Traffic Vance for banners and pop ups https://www.futureads.com/ & https://www.trafficvance.com/ - Lead Impact for pop ups http://leadimpact.com/ - Advertising.com for banners and text ads (yes, an AOL company powers a lot of adware) https://www.advertising.com/ - Ad Peak http://adpeak.com/ for banners, text ads, pop ups, and ecommerce (like Superfish) (they seem to do a lot of both distribution and monetization) - 50onRed (as adwarekiller mentioned) for banners, text ads, pop ups, and ecommerce http://50onred.com - Superfish for ecommerce http://superfish.com - AdOn for text ads, pop ups, and email http://www.adonnetwork.com/
Both Yahoo and Google are in bed with the adware companies via search reset deals and white labeled SERP pages.
There are a lot more companies in the ecosystem. It's massive. A good rule of thumb right now is that if a company advertisers they have cut a deal with an adware company (either directly or indirectly). As you can see from the above list, there is also A LOT of VC money in the ecosystem. The reach extends further when you consider companies that get benefit, like CPXi (http://www.cpxi.com/), AppNexus (http://www.appnexus.com/), OpenX (http://openx.com), or even Amazon Web Services, Google Apps, etc. since these services usually power the business, too.
http://www.benedelman.org/ is a good source to learn more.
Here is a breakdown of IronSource's install tactics: http://www.benedelman.org/news/021815-1.html
If you'd like to talk more, let me know.