There is a ~24% gap between the price you pay in ARS for credit card purchases in USD and what the USD sells for in the black market. This opens up all sorts of arbitrage opportunities that the government struggles to plug.

If you have USD in cash, you can sell them for close to 10 ARS and then buy BTC at about 7.34 exchange rate.

Credit card purchases are charged the official USD exchange rate ~6 ARS + ~20% (the real exchange rate, or the one everyone accepts in the streets is ~10 ARS). The government will pay the difference for no logical reason, consider it an irrational player. And for even stranger reasons people don't realize this, and they also think Bitcoin is a scam, no matter what you tell them. Therefore nobody does this Virwox trick and it stays under the radar, undetected for years.