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Wireless Sensor Networks (WSNs) are susceptible to a wide range of attacks due to their distributed nature, limited sensor resources, and lack of tamper resistance. Once a sensor is corrupted, the adversary learns all secrets. Thereafter, most security measures become ineffective. Recovering secrecy after compromise requires either help from a trusted third party or access to a source of high-quality cryptographic randomness. Neither is available in Unattended Wireless Sensor Networks (UWSNs), where the sink visits the network periodically. Prior results have shown that sensor collaboration is an effective but expensive means of obtaining probabilistic intrusion resilience in static UWSNs. In this paper, we focus on intrusion resilience in Mobile Unattended Wireless Sensor Networks (μUWSNs), where sensors move according to some mobility models. Note that such a mobility feature could be independent from security (e.g., sensors move to improve area coverage). We define novel security metrics to evaluate intrusion resilience protocols for sensor networks. We also propose a cooperative protocol that - by leveraging sensor mobility - allows compromised sensors to recover secure state after compromise. This is obtained with very low overhead and in a fully distributed fashion. Thorough analysis and extensive simulations support our findings.