This is an unexpected day off for the 33,000 students in Iowa’s largest school district.

Officials with the Des Moines Public Schools canceled classes for the day after what’s described as a possible cyberattack on Monday. The suspected breach forced the district to shut down its computer networks as a precaution while I-T staffers investigate what happened.

Classes were called off as those networks support both online and in-person learning, though sports and activities are still scheduled. Last year, Cedar Rapids schools were hit by a cyberattack and paid an undisclosed ransom after losing a week of summer school.