Many people have lost some data while reformatting a computer hard drive. Jered Kenna lost more than that. In 2010 he erased from his computer 800 Bitcoins that have been worth more than $200,000. Kenna isn't upset: He has plenty more. He says he bought his first batch of virtual currency, 5,000 coins, at 20¢ each. On April 10, Bitcoins traded for as much as $258 each, according to Tradehill, a Bitcoin exchange in San Francisco, before plunging more than $100.