United Airlines blamed delays and cancellations of flights Friday night on a "network connectivity issue" that led to a nationwide computer outage. It started around 5:00 p.m. PT, and lines quickly formed in airports in San Francisco, Los Angeles, Denver, and Chicago. It wasn't until 10:00 p.m. that the airline announced via Twitter that the glitch had been fixed. In Los Angeles alone, 2,500 passengers had their flights delayed or cancelled. Airline officials warned passengers delays could spill into the weekend.