The Megamedes Project stored at least one zerg organism in crates at outpost LV-555. They planned on separating one of the zerg from the other organisms.
In March 2499 resocialized Confederate marines were assigned the task of moving crates (containing zerg, which they didn't know about) from LV-555 and putting them aboard a battlecruiser, the Hephaestus. The data was put aboard the battlecruiser as well. However, the creature got out, prompting the marines to make an SOS call.
A high-ranking official passed a set of orders to Center for State Security bureaucrat Tamsen Cauley. He in turn summoned the War Pigs, a group of disposable outlaws used as special ops forces. They were ordered to board the vessel, collect the hub drive and destroy the ship plus anyone else on it.
The War Pigs were successful in their mission, and the Hephaestus disintegrated in orbit. The War Pigs looked at the data and learned about the zerg, months before they became publicly known.