One of the most popular measures of volatility is being manipulated, charges one individual who submitted a letter anonymously to the Securities and Exchange Commission and the Commodity Futures Trading Commission. The letter makes the claim to regulators that fake quotes for the S&P 500 index SPX, +0.26% are skewing levels of the Cboe Volatility Index VIX, -2.50% which reflects bearish and bullish options bets 30-days in the future on the S&P 500 to gauge implied stock-market volatility (see excerpt from the letter below). The flaw allows trading firms with sophisticated algorithms to move the VIX up or down by...