ATM “jackpotting” — a sophisticated crime in which thieves install malicious software and/or hardware at ATMs that forces the machines to spit out huge volumes of cash on demand — has long been a threat for banks in Europe and Asia, yet these attacks somehow have eluded U.S. ATM operators. But all that changed this week after the U.S. Secret Service quietly began warning financial institutions that jackpotting attacks have now been spotted targeting cash machines here in the United States.