its been answered multiple times in multiple places. i'm not sure why people seem to gloss over the answer.

i'll repeat exactly what trap_jaw said:

LimeWire has a authorization feature to create private networks within gnutella. It's deactivated by default but somebody might have activated it in the source code. This will cause older LimeWire versions to display that box.

and then later it said that the code was removed from newer versions, so it shouldn't pop up anymore in the next version.

i have absolutely no clue why you think a text file could be executed and become a keystroke monitor, nor do i have a clue what people would even enter into these popup boxes, because limewire has no username or passwords.