Mars Exploration Must Consider Contamination

letxa2000 writes: "CNN is reporting that the National Research Council has submitted a report to NASA that recommends certain precautions be taken if NASA is to send astronauts to Mars to guarantee that they don't bring back Mars-based bacteria and contaminate earth; including possibly banning the return vehicle from entering the Earth's atmosphere. What is the likelihood of bacterial life on Mars infecting the earth if we ever get around to visiting Mars in person?"