The correct answer is A. Perform a factory reset , because the symptoms strongly indicate a serious mobile malware infection , potentially including spyware or a trojan installed from an unofficial app store. Random pop-ups, excessive data usage, blocked access to banking apps, and inability to update the OS are classic indicators that malicious software has gained deep system-level access .

According to the Quentin Docter – CompTIA A+ Complete Study Guide , mobile malware installed from unofficial sources can embed itself deeply into the operating system, sometimes gaining device administrator privileges. In such cases, standard remediation steps such as clearing cache or uninstalling apps may be ineffective.

The Travis Everett & Andrew Hutz – All-in-One Exam Guide explains that when a mobile device shows signs of persistent compromise—especially when core OS functions and security-sensitive applications are affected—the recommended first step is to perform a factory reset . This completely wipes user-installed applications and restores the device to a known-good state.

The Mike Meyers / Mark Soper Lab Manual reinforces that changing passwords is important after the device is secured, not before. Contacting support or clearing cache does not remove deeply embedded malware.

Therefore, to immediately address the security threat and regain control of the device, a factory reset is the most appropriate first action , making A the correct answer.