United Continental Holdings Inc. risks losing more customers, especially business travelers, after flight delays ensnared thousands of passengers in the third computer failure this year at the world's largest airline.

A software breakdown in United's dispatching system disrupted service for about two hours and initially threw about 250 flights behind schedule, said Rahsaan Johnson, a spokesman. Delays cascaded from there to affect hundreds more planes while Chicago-based United restored regular operations.

The breakdown followed computer malfunctions in March and August that prompted Chief Executive Officer Jeff Smisek's pledge last month to win back travelers who switched airlines because of chronically tardy flights. Business travelers, who fly often and usually pay the most, are considered particularly susceptible to changing carriers because of their job needs.