Madware
Madware (mobile adware) usually finds its way onto a mobile phone through the installation of a script or program and often without the consent of the user.
The purpose of most forms of madware is to collect data from your phone in order to spam you with ads. Most madware variants include an element of spyware, which collects information about internet usage and sends it on to a third party. This data may include details about location, used passwords and contacts.
Prevention
Updated operating systems and spam filters can help protect devices against adware.