Virtual backbone structures are of fundamental importance in mobile ad hoc networks (MANET) as they are essential to support various applications such as service discovery and provision, multicast, routing, etc. In this paper we consider a very natural approach for the creation of virtual backbones, based on weakly-dominating sets, and investigate its security properties against Byzantine adversaries that can corrupt up to a given threshold of nodes. We formalize the notion of secure protocols for the creation and management of virtual backbones, and design a distributed protocol generating weakly-dominating virtual backbones, that is both efficient, according to standard MANET metrics, and secure against Byzantine adversaries corrupting up to a given threshold of nodes.