it is mosaic theory but the information was also the result of a crime (stalking is a crime in NY state) so there is a basis that the info was obtained by way of an illegal activity. since the info was obtained as a result of a crime and would not have been attained any other way, it would likely be considered insider info and trading on that info is therefore illegal. i’m assuming there is no precedence set for this type of activity so there would be lengthy court case to come to a conclusion such as that. if this were done in a state where there are no stalking laws, i would assume there is no basis to say this is an illegal activity.
Gekko also went on to extort Wildman with that information which would help land Gekko in jail anyway. Wildman could have easily dumped his stock to burn Gekko (which Wildman says is an option in the movie) but due to his love for Anacott he accepts Gekko’s premium offer.