  We present a study of anonymized data capturing a month of high-level
communication activities within the whole of the Microsoft Messenger
instant-messaging system. We examine characteristics and patterns that emerge
from the collective dynamics of large numbers of people, rather than the
actions and characteristics of individuals. The dataset contains summary
properties of 30 billion conversations among 240 million people. From the data,
we construct a communication graph with 180 million nodes and 1.3 billion
undirected edges, creating the largest social network constructed and analyzed
to date. We report on multiple aspects of the dataset and synthesized graph. We
find that the graph is well-connected and robust to node removal. We
investigate on a planetary-scale the oft-cited report that people are separated
by ``six degrees of separation'' and find that the average path length among
Messenger users is 6.6. We also find that people tend to communicate more with
each other when they have similar age, language, and location, and that
cross-gender conversations are both more frequent and of longer duration than
conversations with the same gender.
