He said "almost certainly". If Skype could not eavesdrop on calls, they would most certainly say so when ask —because not saying so would make them look bad.

He said "almost certainly". If Skype could not eavesdrop on calls, they would most certainly say so when ask —because not saying so would make them look bad. It's then a simple matter of probability theory to deduce that their silence most probably means it can eavesdrop on calls. Affirming a disjunct is perfectly legitimate approximation in this case.