So many comments asking why people don't use credit cards. The easy answer, already told, is that many Brazilian people don't have bank accounts or credit card.<p>This is only half truth and probably not relevant to the case here, as the malware in question will only affect people accessing their bank accounts through the internet.<p>The "boleto" system is actually a very nice way to handle payments. The boleto mostly substitutes mailing checks: the company I owe send me the bill with a numeric code (and a corresponding bar code for convenience), and I can use this code to pay the bill at a bank, supermarket, lottery houses or, of course, directly from my bank account through the internet or ATM.<p>A boleto is different from a account deposit because each boleto is unique: the code identifies who that specific boleto was sent to, so payment processing is done automatically. No out-of-band bank codes or check handling involved.<p>Boletos are used in several contexts where a credit card is not appropriate, such as paying the credit card bill. However, it may substitute credit cards sometimes: an online commerce outlet will happily generate a boleto for you to pay instead of paying with credit card. You can then pay for you purchase without revealing personal information, having a credit card or sending checks by mail.<p>Actually, paper checks are very, very rare in Brazil nowadays, even in business contexts. Most retail business won't accept them anymore.<p>Also, when you pay a boleto, you get an timestamped authentication code proving you paid it. The company can't allege the check was incorrect, for example. The code may also carry the amount to be paid and/or expiration date, preventing payment of the wrong value of after the due date.<p>This is actually a very functional system that credit cards cannot completely substitute, even if everyone had a bank account or credit card.<p>EDIT: clarity and a bit of extra info