Giving talks on ongoing, unpublished research (dangers of getting scooped?)
Getting ideas stolen is a common fear when starting out (or at least all my Ph.D. students had that worry, and I did too when I was one) but it is much less common that one would think. While the risk does exist, the benefits of opening your research to get feedback from other people greatly outweigh it. Keeping your research secret is just not worth it.

In any case, if you want to reduce the risk, something that you can do is (paradoxically) open up even more! Announce the talk at your website, put your slides online, tweet about it, etc. This means that there will be publicly available evidence that you had ongoing research on topic X by date Y, so prospective scoopers would be easily exposed.