What is the proper response when a professor teaches a side topic related to the course but the information is wrong?
If the teacher is not a reasonable person, and some are not, you should keep your head down and hope that your fellow students will get some real security training, at least on the job, before making decisions in this area.

If the teacher is reasonable, select a very small number of references on the topic, preferably including peer-reviewed papers. Look for an opportunity to talk with the teacher privately, definitely not in class and preferably without any of your fellow students nearby.

Explain that you have had to learn about some security issues because of your jobs over the last 10 years, and that you have more up-to-date information than is being presented in class. (Yes, I know something of the history of security-through-obscurity, but we are being tactful here). Offer your references. How you play it from there on will have to depend on how receptive the teacher is, and how helpful you are willing to be.