Thank you, both.
As far as updating is concerned, I wouldn't install anything from this bunch of
s if my life depended on it.
Slightly oddly, Pprune appears to be worse affected than other sites - having changed forum/thread about 30 times, only 2 were left unaffected by this unasked for interference.
Have just done a search for 'flash' and turned up about 50 instances of various sorts. Top of the list was "Install Flash Player" - that has now gone to the Recycle Bin, so maybe, just maybe ... but I won't hold my breath.