Zango is a tool bar, once installed, it shows some advertisement on users computer.
Zango PPI (per per install) program pays webmasters and software developers to bundle the toolbar with their software or on web site. Zango pay webmaster $0.75 when some one from US install the tool bar on their computer, they pay a lesser amount, some thing like $0.1 when some non-US visitor install the tool bar.
Many adult site use Zango gateway, so visitors need to install the tool bar if they need to access content of the web site.
Zango is relatively clean pay per install program. There are some other program that do some black hat things like cookie stealing and much more.
If like having screen savers on your computer, you may already have some of the PPI program or adware installed on your PC as many of the per per install programs are bundled with such free software.
You can find more about Zango
On google search, i found a link to fbi
