PLINK.EXE is part of the PuTTY family, and it’s the utility tramp is communicating through.
“Burying” the respective tramp buffer in emacs is another one.
Update 2016-02-09:
Actually burying the tramp buffer in question is my 1st approach on all platforms (Linux/Mac/Windows), whenever tramp communication seems to be stuck. Afterwards (with a “clean new start”) everything is fine again in like 99% of the respective the cases.