The Genesis device was a technology designed by Doctors Carol and David Marcus to highly accelerate the terraforming process of a lifeless moon or uninhabitable planet. However, the device could be perverted into a powerful weapon if used where life already exists.
One of Kruge's crew, Karamark vestai-Treth, secretly an officer of Klingon Security, clandestinely transmitted Kruge's stolen data to Klingon Security headquarters on Qo'noS. The data, along with Kruge's death, prompted the Klingon High Council to send an envoy to the Federation demanding the extradition of James T. Kirk. (FASA RPG: Star Trek IV Sourcebook Update)
Following the incident on the Genesis Planet, the Romulan Star Empire increased their intelligence activities to learn if the technology would threaten the Empire. Several of the more powerful families within the Orion Colonies formally censured the Federation after the restriction of space traffic through the Mutara sector. Tensions also grew between Starfleet and the scientific community, despite assurances from the Secretary of Starfleet that the Genesis Project had not been intended as a military operation. The response to this criticism was a media blackout and prohibition of non-authorized discussion of the matter. In further response, joint civilian/Starfleet science efforts were dispatched to both the remnants of the Genesis Planet and the cave laboratory within the Regula planetoid. (FASA RPG: Star Trek IV Sourcebook Update)
Circa 2310, Dr. Carol Marcus created a modified Genesis Device, which was to be tested on the planet Pacifica. These tests were halted when a race of sentient beings were discovered hidden in the depths of Pacifica's ocean. (TOS short story: "The Hero of My Own Life")
In an alternate timeline, a modified Genesis device was used by the Separatist Movement as a planet-killer weapon in 2410-2413. This device was used successfully on Andor, Cardassasia, Trill and Betazed, and was almost used on Earth. (Typhon Station)