Terrorist attacks in Brussels cause some uncertainty in the markets today. The Dow 30 finished in the red by 40 (-0.23%), the S&P 500 lost 1 (-0.09%), but the Nasdaq 100 was able to hang on to a small 12 point (0.27%) gain.Shares of American Airlines (AAL  ) were under pressure (-1.63%) following the deadly terror attacks in Belgium. The company says initial reports indicating that one of the explosions occurred next to the airline's check-in area at the Brussels International Airport are inaccurate. Other travel stocks are taking a hit as well, including Expedia (EXPE  ) - 1.77%, Delta Air Lines (DAL  ) -1.46%, United Continental (UAL  ) -1.14%, and TripAdvisor (TRIP  ) -2.54%.

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Facebook (FB  ) saw a small 0.36% rally today as the social media giant activated its 'safety check' feature after the deadly attacks in Brussels. This marks the first time that Facebook has turned on the alert in Belgium, according to a report by Belgian newspaper Le Soir.

In other terrorist related news, Apple (AAPL  ) gets a rally today (0.76%) as the U.S. Justice Department said that it might not need Apple's assistance in opening an iPhone used by a gunman in the San Bernardino attacks last year. The disclosure led a judge to cancel a court hearing that was scheduled to start today.