There was no extra window - asking for confirmation - by y ?! y was only shortly visible during backup of /home - folder. It was while I was offline. During backup y dissolved into air. I asked around and a prof said, that y is like a rootkit which can only succeed, when BIOS is given (because BIOS has reservated address-space for "y-noobs" ... ). Nah, it seems fortunately not to be dramatic.