[Brad from Tennessee]

This started in the 1980’s. It was blamed for the October 1987 crash. Since then HFT has accounted for more and more of the volume:

http://topics.nytimes.com/topics/reference/timestopics/subjects/h/high_frequency_algorithmic_trading/index.html

[M1903A1]

I may be mistaken, but I believe what was involved in the 1987 crash was simple automated computer trading...the decline levels exceeded the parameters of the programs, and since they had no floors or stops included they just kept selling and fed into the downward spiral.

High-frequency trading that effectively games the exchanges is a comparatively recent phenomenon, within the last few years.