Hundreds of Alaska Airlines flights and thousands of passengers’ travel plans were disrupted over the weekend and well into Monday following a “significant IT outage” that resulted in the grounding of planes for about three hours.

The outage was a result of an unexpected hardware failure in Alaska's data centers and is not related to cybersecurity issues, the airline said.

Alaska Airlines flights were back late Sunday night after an IT outage forced the company to ground all flights for three hours. From 8 p.m. until 11 p.m. PST, Alaska Airlines planes were on hold. The airline did not reveal the nature of the outage.