Deep within The Hive, you'll reach the main research labs where the G-Virus is stored. This area is heavily protected by automated defenses (turrets) and a new type of BOW: the G-Adult. G-Adults are large, slow-moving creatures that can absorb a lot of damage and have powerful melee attacks. Aim for their exposed eyes or weak points on their bodies.
The G-Virus sample will be located in a secure containment unit. You'll need to disable the security system, which might involve activating multiple consoles in different parts of the lab while fending off waves of enemies. Once the containment unit is open, interact with it to retrieve the sample. Be aware that retrieving the sample will likely trigger a massive enemy spawn, including multiple G-Adults and Lickers. Prepare for a prolonged defense.