I used to have a favorite recipe that was a "family secret". My brother-in-law's wife begged me for it for months and promised to keep it a secret. Finally, I relented and gave her the recipe. By the next meeting at the KH, she had blabbed it to everyone in our congregation. That was the last time I shared any kind of important information with HER or her husband, or anyone else I didn't know very well.
BTW, I ended up modifying that recipe, and now it's even better than it was before - it's the fat-free version!! (and I hope my BIL's wife packs on 5 pounds every time she makes the old version!)