Abstract
Communicating Hierarchical Transaction-based Timed Automata have been introduced to model systems performing long–running transactions. Here, for these automata a security concept is introduced, which is based on a notion of opacity and on the assumption that an attacker can not only observe public system activities, but also cause abortion of some of them. Different intruder capabilities as well as different kinds of opacity are defined and the resulting security properties are investigated. Security of long–running transactions is defined by the mentioned notion of opacity and conditions for compositionality are established.