United Airlines issued a systemwide travel waiver, late Friday night due to airline's major computer system outage that caused flight delays and cancellations.

Customers who have already started travel on an itinerary can make one change to their trip without a fee as long as the origin and destination cities are the same and the trip is taken within 7 days. 

Customers who have not yet started travel on an itinerary can make one change to their itinerary, including changing the origin and destination without a fee, however original booking code restrictions apply, meaning the new flights must have the same fare class available.

The airline is also offering refunds to passengers whose flights were cancelled.

The dates of the travel waiver are from June 17, 2011 - June 18, 2011 for tickets purchased on or before June 17, 2011.

The travel waiver is systemwide including major hubs like San Francisco (SFO), Los Angeles (LAX), Chicago (ORD), and Washington Dulles (IAD).

In a statement, the airline said, United apologizes for the disruption caused to travelers at affected airports and is reaccommodating travelers where necessary.

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Update: This article was updated 6/18 11:40 AM, for updated travel waiver information from the United Airlines website.