Wow man! I finally found it and you didnt help me at all
Limesurvey had it itself and this means it is legal since limesurvey had it
Thank you for wasting my time!

Seriously?

This is free software, I am a normal user, just like you. I am trying to give something back to the community by "wasting" my time in the forum to try to help out others and to keep the forum empty from spam. Often successful, often without success.

However, I am deeply sorry for wasting your valuable time by not being able to answer your question.

In order to not "waste" the time of others again: would you mind to explain your solution on the forum, so that other users with the same problem have a solution and I don't have to waste their time?

When i did the survey, there was an option in the edit button in its subdomain named "General Settings" than you choose the tab "Publication & Access Control"
Choose the "Start date/time:" of the survey and than "Expiry date/time:" of it.
Than below is "Set cookie to prevent repeated participation?" and choose yes.
Done!

Hmmm, well, yes. That would have been a solution.

However, I thought you really, really wanted to prevent them from taking part a second time, as you even wanted the MAC address.

So my assumption was that a cookie based solution will not do the trick.

Because obviously it is easy to delete cookies. But if that is what you were looking for, perfect. Problem solved.