Minesweeper

I recently upgraded my laptop to Windows 10.  One disadvantage is the classic minesweeper game has gone away.  Fortunately I can still play it on an older desktop running Windows Vista.  I recently had to create a new account on this machine because a malware infection had rendered my previous account unusable.  This meant my minesweeper win rate statistics were reset and I could easily track my recent performance.  I have since played 100 games on the difficult (16x30) board of which I won 43.  Most of the losses were due to unavoidable guesses but I sometimes trigger a bomb unexpectedly due to flagging a square as a bomb incorrectly.  These errors are most commonly caused by failing to notice a diagonal adjacency.  Taking this into account I estimate the win rate with optimal play is around 50%.