Teams of students from MIT and Britain’s University of Cambridge will spend the weekend hacking one another’s computers, with the blessing of their national leaders. The two schools are competing in a hacking contest that president Barack Obama and British prime minister David Cameron announced last year among other joint cyber security projects. The contest will be hosted at MIT starting Friday. But instead of facing off against each other, the schools are placing their top hackers on teams made up of students from both institutions. For 24 hours, teams will try to hack into one another’s computers to steal a trove of files. Winners will receive prizes topping $20,000.