The SharedCoin and CoinJoin programs are not as safe as you think, according to Kristov Atlas: "...And he's created a new tool to prove it. CoinJoin Sudoku allows a user to match ingoing and outgoing payment amounts, which makes it much easier to discover who is sending funds to whom over SharedCoin. Atlas plans to release CoinJoin Sudoku in two weeks' time, to allow users enough of a chance to move their funds out of SharedCoin and CoinJoin into a more secure and private location."