‘Virtual gold’ may glitter, but mining it can be really dirty

As the poster child for the growing ranks of computer-generated currencies, bitcoin’s recent stratospheric price rises have propelled it from the chat forum-hosted depths of nerddom into the global consciousness. As it rose from under $1,000 to over $19,500 at one point this year, hordes of tech-savvy punters have rushed in to buy, while any investors…