From microsoft.com
Toll fraud malware, a subcategory of billing fraud in which malicious applications subscribe users to premium services without their knowledge or consent, is one of the most prevalent types of Android malware – and it continues to evolve.
Compared to other subcategories of billing fraud, which include SMS fraud and call fraud, toll fraud has unique behaviors. Whereas SMS fraud or call fraud use a simple attack flow to send messages or calls to a premium number, toll fraud has a complex multi-step attack flow that malware developers continue to improve.