The FBI and New York State Police are investigating a cyber attack targeting the Holley Central School District.
Superintendent Robert D'Angelo tells 13 WHAM Rochester an office secretary discovered the district's computer system was attacked in April.
More than 150 current employees and contractors and thousands of past employees and contractors dating back to 2004 were targeted.
It is not believed any personal information was stolen.
The district is now offering free Life Lock credit protection to all employees for a year.
The district's computer system is now more secure than ever before, D'Angelo said.