In a dank auditorium surrounded by high walls and razor wire in Mexico City, a dozen men in beige clothing are writing down the three most common ways they believe that HIV is transmitted. Tattoos, syringes and unprotected sex are among their answers.

“There are a lot of myths and not much information,” says Guillermo Huerta, whose participation in a pioneering effort to increase Aids awareness earns him a little extra freedom during his sentence for robbery with violence. “We plant seeds of knowledge among a vulnerable population.”