We address the problem of attack detection and attack correction for multi-output discrete-time linear time-invariant dynamical systems under sensor attack. More specifically, we focus on the situation where adversarial attack signals are added to some of the system's output signals. Algorithms for sensor attack detection and correction are presented using the notion of 'security index' which characterizes the system's vulnerability against such attacks. The results are illustrated by examples involving multiple sensors. (C) 2018 Elsevier Ltd. All rights reserved.