It is practically not possible to avoid such cases completely. Collaborators must trust each other, but scientific misconduct, e.g. the theft of ideas, happens from time to time. Scientist are morally not better than humans in general. If there is an ombudsperson for scientific ethics or something like that in your institution, and if you are able to provide proof for scientific misconduct (which is hardly possible in your case), you may approach that person. The only real recommendation I can give is to avoid collaboration with these colleagues in the future.

Scientific misconduct in general is a widespread problem, although it is done only by a minority of researchers. See also these discussions:

https://www.researchgate.net/post/How_big_of_a_problem_is_scientific_misconduct

https://www.researchgate.net/post/Lets_talk_about_some_bad_practices_in_Research

https://www.researchgate.net/post/Do_you_know_what_a_paper_mill_is

https://www.researchgate.net/post/Fraud_by_Numbers_Metrics_and_the_New_Academic_Misconduct

https://www.researchgate.net/post/Are_federal_funding_agencies_insensitive_to_data_fabrication

https://www.researchgate.net/post/How_to_address_academic_dishonesty_and_pressures_to_complete_PhD

https://www.researchgate.net/post/What_action_can_you_take_against_someone_who_has_published_an_article_in_a_journal_but_did_not_give_you_a_rightful_authorship

https://www.researchgate.net/post/Is_there_any_one_to_defend_Honorary_forced_authorship_if_not_why_we_practice_it

https://www.researchgate.net/post/Papers_from_research_work

https://www.researchgate.net/post/Is_it_morally_right_or_wrong_for_reviewers_to_propose_articles_unrelated_to_your_work_for_you_to_cite

https://www.researchgate.net/post/Have_you_ever_felt_pressured_by_peer_reviewers_to_cite_seemingly_superfluous_studies_in_your_work

https://www.researchgate.net/post/Unethical_act_of_Reviewer

https://www.researchgate.net/post/Unethical_ways_to_increase_citation

https://www.researchgate.net/post/Can_plagiarism_be_completely_prevented_in_the_academic_world_If_you_think_it_can_or_cannot_be_blocked_Why

https://www.researchgate.net/post/Academic_Fraud_beyond_FFP_Yes_No_or_Anything_Else

https://www.researchgate.net/post/Research_Ethics_in_Publishing

https://www.researchgate.net/post/Can_open_science_decrease_scientific_misconduct

https://www.researchgate.net/post/Unethical_behaviour_in_research_publications

https://www.researchgate.net/post/How_can_the_research_community_detect_and_filter_Balloon_Professors_who_use_their_students_as_their_ladders_without_any_contribution

https://www.researchgate.net/post/In_your_opinion_dont_we_need_a_World_Prize_like_Nobel_Peace_Prize_to_discourage_Frauds_and_misconducts_in_Sciences

Scientific work requires that your work at some point will be exposed and published. There is no way around it. You have to show your work to a journal or a publisher or a professor and have them review your work. Like in your case you had to show it to your teacher. Here Wolfgang R. Dick is right, you should stop cooperating with them and basically lose that specific idea. How much is lost depends either on economic or academic credit. I assume that your case is more of the academic credit. Considering if your work/idea quality is dust collection or free thinking or in between (like research manager, or cathedral builder idea) is what is important in your reaction. If it is first, just let it go. If it is the latter, you should fight for it. You should be able to judge the quality of that idea. Let me share with you my case, I solved the pressure at great depth  in the ocean.  My paper was rejected by a reviewer.  Later I found that my solution was taught at Northwestern University by Sandip Ghosal insinuating that he made /had the original idea. When I contacted him he simply ignored me.   He even uses the same nomenclature as my work. So I believe that he was the reviewer. Now I put his name in my books and everywhere I can in regard to this incident.    In your case, if you can prove that it is the case, publish this guy's name.  You have to be ready for a lawsuit if it is wrong. If you cannot just drop it, life has many other things to offer. 

Hello Nicolò M. Villa

What you describe is most unfortunate and disappointing. Outside person, I can believe (and also advise to reveal as little as possible); inside person is really unfortunate situation - you would expect it would not happen to you like that. Maybe it is a sign you should look for work elsewhere if possible.

I agree with Genick Bar-Meir that firstly, you have to decide how much it means to you and being prepared for the legal standoff which is seemingly inevitable and to take every opportunity to "name and shame" if that is the path you wish to pursue.

Hi All

I think many of us here, have been the victim of such acts, by those who once had superiority over. Bad news is as others added, you almost can do nothing. In very special cases you may complain to univ authorities or take the case to courts, of course in reference to judiciary system of your country (but not these ones you talked about).

But a very good news for you is that, at the age that you are, young and energic, have had ideas, manuscripts, findings, topics... that were important enough that others, such as the professor you talked about "took it".

On the other hand in both cases you talked about, they can not generate new ideas to publish, so they took yours. they may take or steal others. I know that how frustrated you might have been because of those unethical acts.

Every where I say Science Never forgets, Never Forgives. So one day a science whistleblower will act against them. As it is being done and many of them all around the world have been defamed

In your bio you wrote "...I prefer developing solutions with a social impact..."

• So with this soul that you have for "social impact" I can say you have lost nothing, but all gains. Simply be cause you can "generate new scientific ideas" to work as a piece of research. But the ones you talked about can not.
• Also in regard to your last question, may be working in a small team, or by yourself are the best options. By team I mean those, that you trust or should wait to trust.
• I think if you go through a small topic of your interest and research about it, maybe a year or two years later you will see the unseen, more and more problems in that small topic will be reviled to you, not only others didn't know, but you yourself did not know. But after considerable work you will know, while others still don't, all because you worked on a small topic, but not topic or topics.