What is pay per install?
The payperinstall model allows software publishers to monetize software installs, even when the software is distributed free of charge. To earn money with pay per install, you have to bundle your installer with the advertiser's software. Each the an end user decides to install the advertiser's software, you will earn money.
How much can I earn with pay per install?
The amount paid for each install is determined mostly by the user's country. For installs from the United States, Canada and some Western European countries, it is possible to earn amounts in the $0.50-$2 range.
Is pay per install safe for my users?
This will depend only on what pay per install program you decide to go with. There are many that will bundle adware and spyware with your installer and you should be extra careful not to go down that road. However there are also legitimate companies that bundle safe and known software. These pay per install companies might be harder to get into and you have to provide legal traffic, but it is definitely worth it in the long run.