A market exchange where bitcoins can be bought and sold.
The only currency traded for bitcoins by this service is BRL (Brazilian Real).
On March 28, 2013 the service shut down citing losses from a security breach.
That same year, the service's founder partnered with entrepreneurs that finished reimbursing injured customers after the attack. They also invested in technology and security so that Mercado Bitcoin could get back on track. 
Nowadays, Mercado Bitcoin trades Bitcoin and altcoins.