You hear about it all the time - contraband getting smuggled into prisons. It's not unusual to find inmates yakking on personal cell phones, getting access to cash or having a stash of drugs hidden away in their cells.

But have you ever wondered: with so much security, how in the world does all that stuff actually get in there? There's no doubt some places suffer from corruption. But for authorities in Sao Paulo, Brazil, the answer is for the birds.

Officials in the Latin American country have discovered to their stunned surprise that prisoners at one facility had trained carrier pigeons carrying pouches on their backs to fly out of the yard to specific destinations, get loaded up on illegal goods and fly them back behind bars, skipping the watchful eye of guards.

"We have sophisticated equipment to search people when they go in, but they avoided this by finding another way to bring in cell phones and drugs," explains prison director Luciano Gamateli.

The birds live on the jailhouse roof and prisoners were able to smuggle them out using friend and families.

It was an ingenious plan and it worked - for a while. How did officials get wind of the winged wrongs? Guards began to notice an increasing number of birds at the prison were having trouble flying, weighed down by the excess pounds of their unexpected cargo.

It's not immediately clear how they expect to stop the birds from coming and going but they're now doing their best to at least clip the wings of the prisoners behind the clever scheme.