Microsoft apparently has a cardboard VR headset, similar to the Google Cardboard, and it looks like the company is trying to avoid drawing attention to it. News of the headset broke after it appeared in an image appeared promoting a Russian hackathon; the image has subsequently been taken down, but nothing is ever really forgotten on the internet.
From what we can gather from the single picture, it looks like the VR headset works in exactly the same way that Google Cardboard does. Insert the Lumia smartphone into the slot, fire up the app, and hold the VR headset up to your face. It’s nothing particularly exceptional, but it was promised to every participant at the hackathon who come up with a “successful” idea.
There has been no explanation as to why the picture has been hidden, although it is likely that Microsoft simply wants to keep the existence of the VR headset quiet; it is also possible that the headset was an authorised design made by overzealous organisers.