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U.S. stock market futures reopened at 6:00 PM EST, and they tanked instantly and have been near their lows for the past hour.
Dow futures are down 90 points.
S&P 500 futures are down 8.8 points.
Nasdaq futures are down 23.2 points.
Earlier today, the SEC and major stock market operators confirmed that the markets would be closed again on Tuesday. 
This announcement came after futures trading closed at 9:15 AM.
Wednesday October 31 marks the last day of the fiscal year for mutual funds.  As such, futures activity could be reflecting hedging for any anticipated tax loss selling.