unable to remove annoying application...

Hello,

Everymorning, when I turn my computer on, I gat an alert from norton
antivirus asking if I want to block or permit inernet access of
applications with names such as: Ynn1.exe (everyday a different
one...).
I always block it completely but it doesn't matter, the next time my
computer is on, I get the same thing but the file has a different
name.

I've been trying to remove it and I don't know how to do it!

Does anyone know what is it and if so, how do I remove it?

thank you!!!

Fernanda