Banks large and small are girding for an elaborate drill this week that will test how they would fare if hackers unleashed a powerful and coordinated attack against them. Cyberattacks on the banking industry are growing more frequent and sophisticated and the list of assailants is ever-changing: crime bosses who want money, “hacktivists” who want to make political statements, foreign governments that want to spy on U.S. companies. Jamie Dimon, CEO of the country’s biggest bank, JPMorgan Chase, acknowledged that attacks are becoming more complex and dangerous, no longer carried out by “fairly simplistic” hackers commandeering people’s personal computers.