After a user installs a mobile application from an advertisement, the phone ' s battery...

These symptoms strongly indicatemalware infectionor a malicious app running in the background. The first action should be torun a malware scanto identify and remove malicious components.

FromQuentin Docter – CompTIA A+ Complete Study Guide:

“If a mobile device is overheating and the battery drains rapidly after installing an app, this could point to malware. Begin by scanning the device with a mobile anti-malware application.”