Security stepped up at Wimbledon in Shanghai . Top seed Andy Murray subject of online death threat . Federer makes public appearances two years despite threat . Bidding to protect No.1 ranking from Novak Djokovic .
Security stepped up at Shanghai Masters in China . Top seed Roger Federer subject of online death threat . Federer makes public appearances Saturday despite threat . Bidding to protect No.1 ranking from Novak Djokovic .