Help regarding something

Hello, I'm currently asking for help because I'm still kinda new to these kinds of stuff but recently i've been trying to make some programs and when i released it for public, another group took my work and they added some code to my program to make it look like it's theirs and they did it, to be clear if you try to open my program which came from their site, it opens up a messagebox saying "This program is made by us, visit us at bla bla bla" and opens a browser on your pc that redirects to their site so it's like they are pertaining that they did the work for it, I wanted to learn or know how they did this because i don't want this to happen again.

What do you mean exactly by released your program, you released source code?

Was your program packed/protected?

So basically to be clear, the program i'm referring to is a Game and for some reason after public release after a few days i've seen another site posting it on their site and taking credit for the game pertaining they made it because when you launch the program like i said above "This program is made/released by us visit our website." So in this case, for my future uploads i would be able to do this myself.

Release happen where? If it Android/iOS then just report it to marketplaces. If they have website - then report it by DMCA in Google and they will remove it from search. If they earn money with that programm then only way to sue them officially but its long story and possible not worth it.

Cheat engine