GitHub blog says that from now on your profile can include the private repository contributions on your profile.
When enabled, these can make quite a difference in the number of the green boxes, showing your GitHub activity. Here’s an example from mine. Before enabling those, showing only Open Source contributions:
And here’s one after, including private repository contributions:
Indeed, it is a more accurate representation of my GitHub activity. Given that these days most of my private repository activity happens on BitBucket and not on GitHub, this is quite surprising.