Such methods are difficult to detect, and the truth is that teachers have too much going on in the classroom to worry about what each student is looking at on the internet.
If a student’s intention is to cheat, he or she is going to prevail, even if it means tag-teaming with another student. Students will work together to distract the teacher, and then, one student will be able to cheat using one of the aforementioned methods. It becomes a class-wide affair as the students see that if they cheat, they will have great grades.
Yes, the grades of students who cheat may look great on paper, but the important part is the knowledge they gained—which in this case—there is none. I guess there is some validity in the old adage: An honest C is better than a dishonest A.