What Is the Meaning of the Curse Third Finger?

I am charedi from birth, and I have students who say that the third finger is a curse, and I do not understand why, because if one recites a blessing and counts the words on the fingers, then Hashem’s name comes out on the third finger, so that is a sign of blessing. But they say that this is not correct and that it is a curse, and they do not want to tell me the meaning of it. Heaven forbid, I never do this, but perhaps it is a curse. Still, I am interested in knowing what the meaning of this expression called third finger is, and whether it has any source at all. Thank you very much, Yael