Cyber-invasion (Silver Nemesis)

In the year 1988, the Cybermen attempted to invade Earth. (TV: Silver Nemesis)

Background
As ArcHivist Hegelia understood, the Cybermen who attacked Earth in 1988 were CyberIsomorphs, "isolated" and modified remnants of the CyberNeomorphs whom had used an alien time vessel to travel back from Cyber-Control on Telos to Earth in 1985. Facing defeat in the war against the Cybermen which they had failed to prevent in 2526, the Cybermen waged a "silent invasion" which was intended to reverse their fortunes by destroying Earth in the past so the Mondasian Cybermen would not invade it and thus inadvertently cause the destruction of Mondas in 1986. Though this plot was thwarted by the Sixth Doctor, resulting in the destruction of the CyberTelosian Controller and Cyber-Control, a number of Neomorphs remained active in Earth's solar system during the 1980s. (AUDIO: )

Behind the scenes

 * The Discontinuity Guide implies that the "CyberIsomorphs" were in fact native to the 20th century, descended from the Cybermen whom left Mondas. It was after they learnt of Mondas' destruction that they attempted to turn Earth into a new base planet.
 * Doctor Who: Cybermen claims that the Cybermen seen in Silver Nemesis were in fact late CyberNomads who used time travel to invade Earth in 1988, separate from the Neomorphs.