  We present an empirical study of the networks created by users within
internet news groups and forums and show that they organise themselves into
scale-free trees. The structure of these trees depends on the topic under
discussion; specialist topics have trees with a short shallow structure whereas
more universal topics are discussed widely and have a deeper tree structure.
For news groups we find that the distribution of the time intervals between
when a message is posted and when it receives a response exhibits a composite
power-law behaviour. From our statistics we can see if the news group or forum
is free or is overseen by a moderator. The correlation function of activity,
the number of messages posted in a given time, shows long range correlations
connected with the users' daily routines. The distribution of distances between
each message and its root is exponential for most news groups and power-law for
the forums. For both formats we find that the relation between the supremacy
(the total number of nodes that are \emph{under} the node $i$, including node
$i$) and the degree is linear $s(k)\sim k$, in contrast to the analytical
relation for Barab\'{a}si-Albert network.
