Yan Goodrin

 hijacked the ship that the Fifth Doctor tracked a Dalek signal. She had escaped from the lunar penal colony. The Doctor used her hacking skills to find the emergency teleport. The Doctor asked her to do one last criminal thing to write a programme to overwrite Rock Lucifer's original virus. (AUDIO: Lightspeed)

The Doctor would eventually discover that Yan, along with many other people throughout history who looked like her, were caused by a group of Time War Daleks who — while on a mission to prevent the rise of Time Lord society on Gallifrey — created a time distortion which created alternate versions of themselves as four un-mutated Kaled people. This time distortion also caused there to be multiple copies of these four Kaleds at various points throughout time and space. (AUDIO: Effect and Cause)