Bitcoin slumped to a new 13-month low on Monday, with the biggest cryptocurrency touching $5173.23 on the Bitstamp platform. Bitcoin was last down 5.2 percent at $5270. The cryptocurrency, and other lesser coins including ethereum and XRP, endured a sell-off last week, with some blaming fears that a “hard fork” in bitcoin cash, where the smaller coin that split into two separate currencies, could destabilize others.