Facebook shares plunged 18.4 percent on Thursday, and it was set for the biggest one-day wipeout in US stock market history.

The nosedive came after the company on Wednesday said profit margins would plummet for many years due to the costs of improving privacy safeguards and slowing usage in its biggest advertising markets.

The social media giant was the biggest drag on the Nasdaq and the benchmark S&P 500 index, also leading the losses in the technology sector that fell 1.9 percent.

At the open, Nasdaq slid 1 percent, to 7,857, falling from Wednesday’s record close.

The S&P 500 index fell 5 points, to 2,840, and the Dow Jones industrial average gained 128 points, or 0.5 percent, to 25,543, buoyed after the European Union and the United States agreed to negotiate on trade.