STICK 4: Viral Factor (S.T.I.C.K: Baiohazado, lit STICK: Biohazard) is the 4 game in the STICK Franchise main series.
It came to everyone as a shock, an event that sends everyone into terror.
The deads are coming back to life.
The first chapter is spent fighting Zombies while playing as David Fomes. After a while, David is confronted by a hideously mutated creature that is controlled by a STICK device. After defeating the creature, the RAIDERS deducts that the STICK is responsible, and went to raid their new base, which is located somewhere in Necopolis (Entirety of Europe).
The STICK is indeed responsible for the outbreak, along with Skyrockets Corp. And the RAIDERS are determined to put an end to the STICK's new ally this time. Carlos, the CEO of the company (who had somehow survived the Tau Cannon blast in Identity Theft) returns to have revenge on the Raiders, but is defeated once again. Carlos escapes, but not before rigging the Skyrockets HQ to self destruct.
While escaping the collapsing building, the Raiders find several STICK Infantries, zombified by the outbreak, whom are still determined to stop the Raiders. The Raiders manages to escape just as the building goes up in flames. They are then confronted by Carlos again, this time piloting a huge war machine. The Raiders fights, and defeats the mastermind for good, and forces the STICK to retreat in humiliation once again.
While the HMF Staffs and RAIDERS members are celebrating yet another success, the scene switches to the ruins of Skyrockets HQ, where Stickler and a few other infantries searches the rubble for something. One W+M1 Unit finds a vial of unknown liquid, and presents it to the General. The screen then goes black, but not before Stickler shows an evil smile...
STICK 4 introduces the Zombies as well as a couple of biohazard-themed enemies such as the W+M1 Unit and Sterilizer. Also introduced genus is the Healers, including Support Medics, Combat Medics and Nightingales.
Particularly Cloud and Flash, whom are near useless in this game because they are unnessecary against the most common enemies in the game: Zombies and Mutants.
- Cloud: Carries the Mass-35 self-reloading Missile Launcher. His Fury is "Nuclear Fusion".
- Flash: Carries the TXG-400 minigun (a scaled up version of the TX-120A). His Fury is "Bullet Storm".
- This is the only game in the main series where an enemy debuting in it did not reappear in later main series. The Zombies did not reappear until STICK 2D, Tactics, and Chronicles. Morever, the Zombie Stick Figures seen in the escape sequence in Mission 10 did not reappear in the franchise at all, making them exclusive to this game.
- The zombified STICK infantries includes the Basic Soldiers, Heavy Weapons Unit, Valkyrie Archers, Assassin Maids, Crusaders, Samurais, Blade Chargers and Shinobis.