The fact that they allowed such a blatant vulnerability to reach production makes me question their test suite and development process. What else is wrong that we are not seeing?
I expect more transparency and professionalism from a company that processes $7.1 billion in transactions.
Security is hard and accidents are easy, dropbox once had a four hour period where they didn't verify passwords!
http://techcrunch.com/2011/06/20/dropbox-security-bug-made-p...
I believe that owning up to your mistake and being transparent about it can only make your customers trust you more. What worries me is that Mercado Pago is huge and they never released a statement about this issue. I hope that they change this policy soon.