UPDATED: 2:50 p.m. ET

Flying United on Wednesday? Not so fast.

The airline grounded all its flights for two hours Wednesday morning, stranding fliers across the country after it experienced a system-wide computer failure. Long lines formed at airports and more than 800 flights were delayed and about 60 were canceled because of the technology problem, according to United.

An airline spokeswoman confirmed that the glitch was caused by an internal technology issue and not an outside threat.

Spokeswoman Jennifer Dohm said that a router problem reduced "network connectivity" for several software applications. "We fixed the router issue, which is enabling us to restore normal functions," she said around midday.

BREAKING: United says issue with router degraded network connectivity for some applications, causing this morning's operational disruption — Reuters Top News (@Reuters) July 8, 2015

United announced that there will be a waiver on fees for passengers who want to change flights, and in some cases the airline will waive the difference in fare for a different ticket.

All @united flights are delayed due to a system wide computer failure. #timetogetamac — Daniel Ball (@daball80) July 8, 2015

They just announced every single @united flight in the country is grounded because their computer system went down #Y2K15 — Brad Pittsburgh (@brad_pittsburgh) July 8, 2015

Now @united airlines pilot offering tours of the flight deck to bored passengers. "We don't have anything better to do" #unitedcomputerfail — Betsy Fischer Martin (@BFischerMartin) July 8, 2015

Waiting at @LAX. @United computer systems down. Huge lines. Will probably miss my flight to NY. Should have chosen JetBlue. — Meni Tsirbas (@MeniThings) July 8, 2015

Photos and videos posted to Twitter showed long lines at airports. Passengers affected by the outage had few options but to wait it out; complaints on social media were proliferating as airport staff and flight crews provided as much information as they could to frustrated travelers.

A similar outage impact United on June 2 when all of the carrier's flights were grounded for about an hour due to a problem with "dispatching information," the airline told WIRED.

@united what's going on?!? All flights and system down? Close to an hour now at the gate. pic.twitter.com/tQrPwYpbvj — brooke (@cbrookewit) July 8, 2015

@united any information available other than "computers are down?" That's not very helpful. — Dave Sobel (@djdaveet) July 8, 2015

Flights began to take off again shortly after 9:15 a.m. ET.

We experienced a network connectivity issue. We are working to resolve and apologize for any inconvenience. — United (@united) July 8, 2015

United suffered a series of computer problems in 2012 after switching to a passenger information computer system previously used by merger partner Continental Airlines.

In each case, hundreds of flights were delayed. A number of high-paying business travelers defected to other airlines and revenue dropped.

At Los Angeles International Airport on Wednesday morning, the line at United stretched up and down the sidewalk outside the terminal.

Welcome to LAX! A photo posted by michaelgards (@michaelgards) on Jul 8, 2015 at 6:56am PDT

A White House spokesman said President Barack Obama was briefed on the glitch and that it appeared unrelated to an outage hours later at the New York Stock Exchange.

"There is no indication at this point either that there is malicious activity involved," said the spokesman, Josh Earnest.

Additional reporting by the Associated Press