A user installed a free application from an unofficial application store.

The symptoms point strongly to a bootleg/malicious application from an untrusted source: random pop-ups (high number of ads), increased data usage (high network traffic/data-usage warnings), and abnormal restrictions such as failing OS updates or blocking access to sensitive apps (unexpected application behavior). These are specifically listed as common mobile security symptoms associated with malicious apps and untrusted APK sources. When a device shows multiple signs of compromise and normal remediation options (like