The proliferation of phasor measurement units, albeit transformative to grid operations, increases the risk of cyber threats in power systems. One consequence of these cyber threats is incorrect operator actions based on misleading data. While a single wrong operator action might not result in a widespread blackout, a series of actions on critical lines and transformers, combined with pre-existing faults or scheduled maintenance, might. Traditionally,  controlled islanding prevents cascading failures. However, it is only effective when the received measurements are trustworthy.