Which event is considered the worst single source of contamination in LEO due to its debris output?

Answer

China's kinetic energy ASAT test in January 2007

China's 2007 test against the FengYun-1C weather satellite created an estimated 300,000 pieces of debris 1 cm or larger, increasing trackable debris by 25% in a single event.

Which event is considered the worst single source of contamination in LEO due to its debris output?
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