Oct 20 NYSE SPY "Mispricing"

Bloomberg:
NYSE Software Glitch Spurs $7.9 Billion Misprice in S&P 500 ETF

A system upgrade at Arca triggered what appeared to be a 9.6 percent plunge yesterday in an exchange-traded fund that tracks the Standard & Poor’s 500 Index, a drop that would have erased $7.9 billion from one of the most popular securities in the U.S. Data published by the electronic venue at 4:15 p.m. New York time showed the SPDR S&P 500 ETF Trust at $106.46, compared with its opening level of $117.74.

The prices were later voided and the closing price updated to $118.54, up 0.7 percent, exchange officials said.