(Bloomberg) -- A plethora of websites operated by financial institutions and airlines including Hong Kong Exchanges & Clearing Ltd. and Southwest Airlines Co. went down briefly Thursday in what appeared to be a widespread internet outage.

Website tracker Downdetector.com initially flagged hundreds of user complaints about an outage affecting Southwest, Delta Air Lines Inc. and Automatic Data Processing Inc. Other websites pinpointed included those operated by Vanguard, E-Trade, Navy Federal Credit Union.

Several of the websites have come back online, including the Hong Kong exchange’s.

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