The Blight
It is not really explained very well.
It is a genetically engineered microorganism with the internal machinery replaced with mechanical supplements that allow it to grow at an insane rate. Able to survive the harsh conditions of New Terra, it is engineered to seek out water and oxygen deep in the rocks. The blight is able to break hydrogen bonds with water, to create H2 and O2(what is desired). This is necessary to make New Terra's atmosphere breatheable. Anything containing water can be broken down by the blight. As such, it is able to break down plastics, and less desireable, people. It also seems to be able to break down organic carbon bonds, such as CO2. This allows creation of C(s) and O2(g)
The blight moves in waves. It spreads very slowly, until a large amount of water and oxygen is built up. The rocks crack (this causes sismic instablilty), and the water surges throughout under high pressure, along with the oxygen. These surges quickly carry the blight along. It then sits for a while, and begins the process all over again.
How the blight was released is only specualted on. The theory is that the blight caused enough pressure build up in the test well that it litterally caused a massive explosion. This explosion threw the blight amoungst the populace at Nuguyen's meeting. Those not instantly killed by the decompression caused by the explosion got to enjoy the slow death, as the microbe broke down their tissues. Some would have died from explosive decompression before the blight finished them, based on how fast it can effect buildings.
I have a theory available.
One thing mentioned in the campaign, blight spreads faster during the day, then at night. Thus, solar radiation, be it light, or some other form, must aid blight growth, but must NOT be required for growth. Hence, the blight may be able to process sunlight (photosynthesis), or solar radiation, such as X-Rays, somehow.
Tanks are lost when infected by the blight because the blight breaks down their plastic seals and their boptronic computer cores. This leaves a basic unit that knows no friend or foe. It can only move, patrol, shoot.
This is all from memory, so some is bound to be incorrect. I will modify as necessary, as new information is brought to my attention.