Wall Street's 'fear index' hit its lowest level in a decade — and it's unclear why

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Something strange happened to Wall Street's so-called fear index on Wednesday.

The CBOE Volatility Index (VIX), widely considered the best gauge of fear in the market, broke below 10 for less than a minute Wednesday at 2 p.m. ET, right after the Federal Reserve decided to keep interest rates unchanged.

While some experts questioned the significance of the move given its brevity, it did mark the first time since Feb. 16, 2007, that the index fell below 10. Experts who spoke to CNBC said the move could have come as a result of an algorithmic glitch or some other anomaly, but it's very difficult to pinpoint the exact cause.

Asked for comment, a spokesperson from the Chicago Board Options Exchange, which calculates the Vix, attributed the move to a "short-lived" wide spread between the bid and asking prices.

The VIX's sudden move "would imply that at the moment the news broke, bids in the strip or option chain were temporarily pulled due to a large order imbalance," said Dan Deming, managing director at KKM Financial. He added that "while the VIX cash had that move, VIX futures didn't really react. That would lead me to believe this was some sort of anomaly."

Randy Frederick, vice president of trading and derivatives at Charles Schwab, echoed Deming's remarks, saying the move "was probably driven by a very large order right at 2 p.m." sent by a high-frequency trader.

He added, however, that the move may not be "a big deal" since it lasted less than a minute, and the index recovered very quickly from those lows.

On Thursday, the VIX was sitting near 12. Wednesday marked just the 17th time the VIX has traded in the single digits.

VIX minute-by-minute chart from Wednesday

Source: FactSet