Chasm City (Revelation Space) by Alastair Reynolds

The once-utopian Chasm City -a doomed human settlement on an otherwise inhospitable planet- has been overrun by a virus known as the Melding Plague, capable of infecting any body, organic or computerized. Now, with the entire city corrupted -from the people to the very buildings they inhabit- only the most wretched sort of existence remains. For security operative Tanner Mirabel, it is the landscape of nightmares through which he searches for a low-life postmortal killer. But the stakes are raised when his search brings him face to face with a centuries-old atrocity that history would rather forget.