A commuter sees a flyer on a train with a QR code advertising high interest rates at an online bank. The commuter scans the code, but the website indicates the promotion has ended. Within a few days, the commuter's phone starts sending messages to everyone in the contacts with a malicious link. How could this have been prevented?

a$.$ Do not scan QR codes from unfamiliar sources.

b$.$ Ensure the antivirus software installed on the phone is up to date.

c$.$ Open a browser in private mode before scanning the QR code.

d$.$ Download and install a secure browser before scanning the QR code.