According to Google’s annual Android security report [pdf], installs of malicious apps from the Google Play Store increased by 100% in 2018. However, the company claims that the reported increase is a result of its decision to start considering click-fraud applications, also called adware, as “potentially harmful apps” (PHAs).
Since adware made up 55% of PHA installs in 2018, the number of malicious installs for 2018 would actually be lower than that for 2017 if click-fraud applications were not included. After adware, Trojans were the most common form of malware, accounting for 16% of malicious installs.
Read more: Google: Malware in Google Play doubled in 2018 because of click-fraud apps