The site itself used to be the only Brazil-based Bitcoin exchange. It's been unreachable for a few days, and hours ago they've sent an ominous email to customers which is circulating as a paste. To quote in relevant part,
O Mercado Bitcoin sofreu um ataque, que infelizmente foi bem sucedido, em sua implementação de redeem code. Devido à um erro de codificação, foi possível ao atacante gerar novos códigos de crédito, sem que o valor fosse devidamente debitado em seu saldo final. Conseguindo assim, gerar um montante falso de bitcoins dentro do sistema e resgatá-lo em tempo hábil, durante a madrugada.
That says their redeemable codes implementation was broken in that it allowed infinite withdrawals. They also say they've lost enough to close doors. Bitcoin holders are likely to take a beheading, fiat holders on the exchange look set for a Cypriot-style haircut.
To quote an older article in relevant part,
The time of cowboy style, “one man and his hopes” fiat-BTC exchanges has passed. The exchange market is moving into a new phase. There is room on it for MtGox, on account of its old age and well known brand, and for people like the Frenchies doing that bitcoin-central partner-with-a-bank thing. All other exchanges are going out, and things being what they are the majority of them will be going out uncleanly.
Because of this, keeping money in any other fiat-BTC exchanges than those two is pretty much cruisin’ for a bruisin’. Spot sellers may still be safe for a while, select ones may even be safe forever (as they’re a subset of the OTC style marketplace), but for better or worse cowboy exchanges are a thing of the past.
So it goes.