According to one expert's recent report, the total number of mobile malware items detected in 2016 increased by three times over the 2015 numbers. Advertising Trojans were the most common mobile malware, representing 16 of the top 20 malware programs identified.
Security experts are finding that these Trojans not only flood the device with continuous advertising, but they can also infect root processes and allow secret installation of other applications, including apps from Google Play. Dave Sachin "Most malware attacks were carried out through advertisements: Kaspersky," economictimes.indiatimes.com (Mar. 3, 2017).