Some consultants may tell you as a free hosting provider, you should stay away from popup or pop-under ads, because such ads may drive genuine users away.
This is not always correct, at least it is often misleading. Using popup ads wisely can monetize your traffic without affecting genuine users.
Yes, you should not put popup ads in normal pages, or your own pages, because most users do not like popup windows. However, these pages are perfect for popup or pop-under ads:
- 404 page. If the page does not exist, put a popup ads before redirecting the user to the main page will not affect most users. Remember, for free hosting providers, you may have 5-10% traffic goes to 404 (page not found). Some free hosting providers never put a 404 page, or directly redirect the traffic to other pages. This is a big waste.
- Suspended pages. You will get a lot of abusers whenever you run free hosting service. You need take some actions to avoid excessive abuses. Once such account is suspended, you can show all visitors a suspended page, and put some ads, including popup or pop-under ads. Usually for abusing account, you should suspend it first instead of deleting it. If you delete it, the abuser can re-register and continue to use the abusing URLs.
- 403 page. If you installed mod security for your Apache server to filter abnormal traffic requests, you should setup a 403 page. If the page is not found, 404 page will be used. Anyway, you can also try to monetize such traffics with popup or pop-under ads.
- Proxified pages. As I mentioned in the Top 5 Adsense rules for free hosting providers, you should not place Google Adsense ad on proxified pages because you have no control on the contents. However, you may put popup or pop-under ads on such pages. As long as you cap the frequency of such ads, users usually do not mind it.
Be reminded, Google does not want to see pop-up or pop-under ads in Adsense pages. So, if a page can put Adsense, you should not put any pop ads, as mentioned as Rule #5 in the Top 5 Adsense rules for free hosting providers.
Anyway, you should maximize your earning potential from non-conventional traffics by using popup or pop-under ads wisely.