The Nasdaq Composite Index Wednesday morning was unraveling, down more than 1.5%, and far outstripping its U.S. equity peers lower, as testimony centered on social-media platforms and their vulnerability to hacking and data breaches on Capitol Hill got under way. Twitter CEO Jack Dorsey and Facebook Chief Operating Officer Sheryl Sandberg defended their efforts to prevent outside manipulation of their social-media platform by Russian and other foreign actors. Still, the Nasdaq [s:COMP] was off by 1.5%, giving up ground at a psychologically important level at 8,000, at 7,971. That morning drop was far steeper than losses for the S&P 500 index SPX, -0.45% down 0.6%, and the Dow Jones Industrial Average DJIA, -0.04% was declining by 0.2%. Testimony from the key internet and technology companies, including executives from Facebook Inc. FB, -1.39% and Twitter Inc. TWTR, -4.36% in front of a Senate panel come as the government continues to investigate the role of social media in the 2016 election won by President Donald Trump. Shares of Twitter were down 6%, while those for Facebook were of by about 1.45. Shares of Google-parent Alphabet Inc.’s clase of shares GOOG, -1.96% GOOGL, -1.87% were both down by at least 2% in morning trade. Google executives declined to attend the hearing.

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