The Kaban Project (The Horus Heresy Series)

The Mechanicum priesthood guards its secrets carefully - few of its technological marvels and processes are fully understood by the Imperium, and many more could be deadly if allowed to fall into the wrong hands. However, in the forges of Lukas Chrom, something sinister has come into being. Rumours abound of forbidden lore and artificial sentience, and a name has been whispered in the dark corners of the Martian data network: 'Kaban'.

Read it because
It's a prequel to Mechanicum which explains the origins of the mysterious intelligent machine that causes havoc on Mars...