  We introduce a subclass of concurrent game structures (CGS) with imperfect
information in which agents are endowed with private data-sharing capabilities.
Importantly, our CGSs are such that it is still decidable to model-check these
CGSs against a relevant fragment of ATL. These systems can be thought as a
generalisation of architectures allowing information forks, in the sense that,
in the initial states of the system, we allow information forks from agents
outside a given set A to agents inside this A. For this reason, together with
the fact that the communication in our models underpins a specialised form of
broadcast, we call our formalism A-cast systems. To underline, the fragment of
ATL for which we show the model-checking problem to be decidable over A-cast is
a large and significant one; it expresses coalitions over agents in any subset
of the set A. Indeed, as we show, our systems and this ATL fragments can encode
security problems that are notoriously hard to express faithfully:
terrorist-fraud attacks in identity schemes.
