Implementations of montgomery's modular multiplication algorithm (MMM) typically mke conditional subtractions in order to keep the output within register of modulus bounds. For some standard exponentation algorithms such as m-ary, it has been shown that this yields enough information to deduce the value of the exponent. This has serious implications for revealing the secret key in cryptographc applications without adequate counter-measures. Much moder detail is provided here about the distribution of output values from MMM when the output is only reduced to keep it within register bounds, about how implementations of sliding windows can be attacted, and about handling errors