The article is a bit sloppy, the filing linked at the bottom explains it much more accurately. NYSE didn't really 'choke' but the trading of some securities was affected. The root cause wasn't really a click or the flood of cancel orders themselves - it sounds like if the Credit Suisse system had actually managed to place all of its orders, the respective cancels would have been handled as well. What happened though is that CS&#60;-&#62;NYSE got into an endless loop of spewing messages at each other because the CS end was simply ignoring the NYSE system's error messages and the NYSE system had no facility to detect a clearly abnormal rate of identical errors being generated by the same client. Bug met inadequately robust design and the whole thing imploded.