China has announced a ban on cryptocurrency transactions, the latest in a string of crackdowns on virtual money that comes as countries around the world consider tighter regulations. SCOTT SIMON, HOST: China bans cryptocurrency transactions. And as NPR’s David Gura reports, it sends shockwaves through an industry valued at $ 2 trillion that is largely immune from government interference. DAVID GURA, BYLINE: Part of the global popularity of cryptocurrency stems from the fact that the digital asset is free from government control. And it really hasn’t been regulated. It is attractive to many Chinese citizens. But Chinese leaders have spent…