(FILES) This file photo taken on May 17, 2012 shows a Facebook logo seen through the windows of the NASDAQ stock exchange in Times Square in New York. Facebook on August 9, 2016 began letting marketing messages slip past ad-blocking software on desktop computers. The update to the leading social network's advertising platform came with assurances that Facebook understands how annoying ads can be and with enhanced tools for controlling the kinds of ads shown to users. / AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

A man walks through Killian Court at the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts, U.S., May 13, 2016. REUTERS/Brian Snyder - RTSF679

A man walks through Killian Court at the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts, U.S., May 13, 2016. REUTERS/Brian Snyder - RTSF679

Members of the mission group Adventures In Missions wait to find out if their flight to Guatemala is on time or cancelled after Delta Air Lines' computer systems crashed on Monday, grounding flights around the globe, at Hartsfield Jackson Atlanta International Airport in Atlanta, Georgia, U.S. August 8, 2016. REUTERS/Tami Chappell

John M. Grunsfeld (L), Associate Administrator for the Science Mission Directorate, poses for a selfie with Ahmed Mohamed, 14, the Texas teenager who was arrested after bringing a homemade electronic clock to school, during the second White House Astronomy Night on the South Lawn of the White House in Washington October 19, 2015. REUTERS/Joshua Roberts

Abby Nass (L) and Cara Martin (R) wait as part of the mission group Adventures In Missions, to find out if their flight to Guatemala on Delta is on time or cancelled after Delta Air Lines' computer systems crashed on Monday, grounding flights around the globe, at Hartsfield Jackson Atlanta International Airport in Atlanta, Georgia, U.S. August 8, 2016. REUTERS/Tami Chappell

The Delta baggage area of the terminal is empty after Delta Air Lines' computer systems crashed on Monday, grounding flights around the globe, at Hartsfield Jackson Atlanta International Airport in Atlanta, Georgia, U.S. August 8, 2016. REUTERS/Tami Chappell

Passengers line up as they wait in the ticketing area after Delta Air Lines' computer systems crashed on Monday, grounding flights around the globe, at Hartsfield Jackson Atlanta International Airport in Atlanta, Georgia, U.S. August 8, 2016. REUTERS/Tami Chappell