  Group centrality measures are a generalization of standard centrality,
designed to quantify the importance of not just a single node (as is the case
with standard measures) but rather that of a group of nodes. Some nodes may
have an incentive to evade such measures, i.e., to hide their actual
importance, in order to conceal their true role in the network. A number of
studies have been proposed in the literature to understand how nodes can rewire
the network in order to evade standard centrality, but no study has focused on
group centrality to date. We close this gap by analyzing four group centrality
measures: degree, closeness, betweenness, and GED-walk. We show that an optimal
way to rewire the network can be computed efficiently given the former measure,
but the problem is NP-complete given closeness and betweenness. Moreover, we
empirically evaluate a number of hiding strategies, and show that an optimal
way to hide from degree group centrality is also effective in practice against
the other measures. Altogether, our results suggest that it is possible to hide
from group centrality measures based solely on the local information available
to the group members about the network topology.
