If you want to taste the fruits of forbidden virtual reality—be it from Steam or from a forum post or some shady website you found—you’ll need to expressly opt in to doing so. Luckily it’s not overly difficult to tear down the walls.
In the main Oculus window (on your normal monitor, not in the headset) go to Settings, then General, and then click the tick box next to “Unknown Sources – Allow apps that have not been reviewed by Oculus to run on my Rift.”
And you’re done!
Here’s Oculus’s reasoning for requiring you to opt into running apps not provided by the Oculus Store:
So in layman’s terms, the risks here are 1) Malware 2) Vomiting 3) Pornography 4) More vomiting, and 5) Tripping and breaking your neck. But who ever let that stop them