@MRB1989 while what you are asking about is very possible with any computer like device, I wouldn't necessarily say it's ever likely to happen. Staying smart when browsing online and using your better judgment is always the best preventative method to keeping your phone secure. That being said, I have been very happy with the security features Samsung provides. :)
@SHADOWGATE I read the article you posted, but I couldn't find the part where they say ultrasonic sensors are "just for decoration" or that they are inherently insecure. It even says the sensor is an "even more secure alternative to capacitive scanners." Also, Samsung Knox has been repeatedly mentioned for it's high security standards.
Keeping a strong password or pin with KNOX running correctly is more than efficient for the daily driver phone which brings me back to my previous statement of "if and when your fingerprint fails to read the security reverts back to those options"