Hackers have staged cyber-attacks on three Greek banks and demanded a ransom in bitcoins, a virtual monetary unit, to stop their disruption, banking sources said on Monday. The sources said the hackers managed to block the Internet banking activity of three Greek lenders for a few hours last Thursday but did not penetrate the banks' security or obtain confidential client data or access to accounts. "All they achieved was to block the web banking for a few hours. Nothing else," one banker told Reuters, speaking on condition of anonymity. The sources said the hackers had given the name of their group as Armada ... (full story)