By Noel Randewich and Julie Gordon SAN FRANCISCO/VANCOUVER (Reuters) – Some savvy bitcoin investors have a solution to cyber-thieves and instability shaking online exchanges: they print out their virtual savings and hide them in the real world. The shuttering this week of bitcoin exchange Mt. Gox and fears that hundreds of millions of dollars worth of the virtual currency have been lost or stolen are pushing investors to tighten their security. Enthusiasts around the world use online exchanges to conveniently buy and sell bitcoins but bitcoin savings can also be kept closer to home. Canadian mortgage broker and bitcoin enthusiast Chung Cheong writes out his secret number by hand and puts it in a safety deposit box.