The SS Hermes spaceship was reduced to a skeletal carcass after a highly corrosive and chameleonic microbe got loose on board and ate away at the very ship itself, killing the crew in the process. Because of this little is known about the Hermes, or the nature of the ship-devouring virus it fell victim to (although it is stated that the virus was synthetic, so it is possible the virus was made in the laboratory of the Hermes).
The deadly microbe then escaped on a pod from the wrecked vessel, along with the lone survivor Talia Garrett (an old acquaintance of Red Dwarf Captain Frank Hollister). The virus was unknowingly taken aboard Red Dwarf along with the escape pod, in the last ever episode, "Only the Good...".