North Shore-Long Island Jewish Health System has sent letters to about 100 patients from its North Shore University Hospital identified by law enforcement authorities as victims of identity theft, the system announced. Details disclosed were limited “because we do not want to compromise the integrity of the investigation,” according to a statement posted last week on the system’s website. The statement noted, however, that nearly 1,000 people throughout the Northeast have been victimized by what it described as an “identity-theft ring that extends ‘far beyond North Shore University Hospital.’” The system is working with New York State Police and the Nassau County district attorney’s office in the investigation and is “taking aggressive steps to further safeguard the security protocols currently in place to protect patient information,” according to the statement. North Shore- LIJ spokesman Terry Lynam said the system first became aware of the breach about a year ago and began notifying patients last July after the arrest of an identity-theft suspect possessing “face sheets,” or patient summaries created at admission for billing and care purposes. They list why the patient was seeking treatment as well as names, addresses, dates of birth, Social Security numbers and, if available, insurance information.