United Airlines grounded all flights due to a "computer system problem."

United Airlines grounded all domestic flights this evening due to a malfunction in the computer system that manages aircraft weight and balance, the company announced.

"Due to a technology issue, we are holding United's mainline flights at their departure airports," an official statement read. "We expect further delays throughout the evening as we work to resolve the situation. Safety is our top priority, and we will work with our passengers to get them to their destinations."

United confirmed to ABC News that this was not a cyber attack.

The grounding does not affect flights operated by United Express and does not affect aircraft already in flight, which will continue regularly to their respective destinations.

According to various communications issued by the FAA, the company has requested takeoffs be halted at several of its major U.S. hubs, including Newark, San Francisco, Chicago, Denver, and Houston.