These contraversial programs are very good source of money. Even when you have site with high traffic and no conversio at all than pay per install will work for you.

There were problems in the past with these programs because some of them were considered as a spyware because they were installing unwanted SW in the computers and changing homepages or changing cookies.

These days programs you see are usualy carefull and they dont want to go against the law. Problems are usualy with webmasters who are cheating somehow and adding some other codes which make problems to PPI companies.

User have to agree first that he realy wants this to be installed on his computer and he knows what will be installed (or should know). Than he will see time to time some poupup. It is like those programs which are paying for surfing the Internet and watching ads. You were yourself watching Ads now other people are watching untill they uninstall this software.

You can talk here about these programs and share your experience.
The Biggest players are ZangoCash, MatCash and TeddyCash.
I know few more but they are not open for public. If you need some details PM me.