The X-Files Season 4 Episode 8

A rock sample taken from Mars is intercepted at an airport and infects a security officer with the Black Cancer, while Mulder is given a tip about potentially dangerous paramilitary operations but is doubtful when the informant turns out to be Alex Krycek. Reluctantly, Mulder accepts Krycek’s help and tracks the rock to Russia where he discovers an elaborate test being performed by Russian scientists.