Amid a flurry of cyber attacks in which hackers have demanded ransom payments from health systems, a top executive at Northwell Health met with FBI officials and federal prosecutors on Wednesday to discuss how law enforcement can help combat this persistent and growing threat. Northwell Health, the largest private employer in the state, is attacked unsuccessfully millions of times each month by computer programs and programmers looking for a way into their system, said John Bosco, the company's senior vice president and chief information officer.