Wandera, a security research firm, has found malware in 17 apps on the Apple App Store. The apps use a clicker trojan module to generate fraudulent web traffic in the background, likely to pump up ad revenue for specific websites. The apps passed through Apple's stringent review process because they connected to a remote server to execute the fraudulent activity rather than having malware embedded directly in their code.
https://www.notebookcheck.net/Trojan-malware-found-in-17-apps-on-Apple-App-Store.440350.0.html