Pay-per-install

Definition
Under a pay-per-install (PPI) scheme, an advertiser pays a publisher a commission for every install by a user of usually free applications bundled with adware applications. Users are prompted first if they really want to download and install this software.

Some botnets are known to operate PPI scams to generate money for their operators. Essentially, the compromised computer with the bot agent is instructed to install the software package from a registered PPI source via the bot's command and control system. The bot operator then receives payment from the PPI agency and, after a short period of time, uninstalls the software package and installs a new one.