Investors are still attempting to understand what caused a trading glitch at Knight Capital Group Inc that roiled markets and wiped out $440 million of the firm's capital.

The incident is hardly the first technical problem to test markets. Here is a timeline of other problems that have hit exchanges in recent years:

Date Exchange Breakdown
8/1/2012 NYSE Technical error at Knight Capital Group roils prices of 140 stocks on the New York Stock Exchange
5/18/2012 Nasdaq Nasdaq fumbles Facebook IPO, creating mass delay in order confirmations and losses as high as $200 million
3/23/2012 BATS BATS withdraws IPO after "software bug" causes a plunge in its shares and a trading halt in Apple
2/13/2012 NYMEX Electronic trading of U.S. oil futures on the New York Mercantile Exchange halts for more than an hour and CME Group's Globex platform freezes due to "technical issues"
2/2/2012 TSE Tokyo Stock Exchange suffers major glitch in cash-share trading, preventing morning trade in some 240 shares and instruments
1/17/2012 JSE Johannesburg Stock Exchange halts equity trading after network glitch
11/30/2011 TSX Toronto Stock Exchange glitch freezes trading of companies whose symbols start
with letters M-Z, affecting high-volume stocks
10/27/2011 ASX Australia's stock market suffers technical failures that halt trading for
four hours
10/26/2011 NYSE NYSE Euronext's calculation of stock Euronext indexes in Paris, Amsterdam, Brussels and Lisbon suspended due to technical problem
8/25/2011 Euronext Euronext says dissemination of France's CAC 40 index suspended due to technical glitch
8/10/2011 Euronext Euronext's dissemination of European stock indexes suspended due to glitch
8/5/2011 FTSE LSE Publication of Italy's blue-chip FTSE MIB index halted for the second time in two days
8/4/2011 NYSE NYSE Euronext hit by a glitch that Euronext affects indexes of Paris, Brussels, Amsterdam and Lisbon
7/29/2011 NYSE NYSE Euronext hit with a glitch as Euronext technical problems halt dissemination of indexes based on European share markets
5/6/2010 All US Dow drops 1,000 points in minutes as markets multiple stocks print prices of $0