  We have previously introduced vertex attack tolerance (VAT) and unsmoothened
VAT (UVAT), denoted respectively as $\tau(G) = \min_{S \subset V}
\frac{|S|}{|V-S-C_{max}(V-S)|+1}$ and $\hat{\tau}(G) = \min_{S \subset V}
\frac{|S|}{|V-S-C_{max}(V-S)|}$, where $C_{max}(V-S)$ is the largest connected
component in $V-S$, as appropriate mathematical measures of resilience in the
face of targeted node attacks for arbitrary degree networks. Here we prove the
hardness of approximating $\hat{\tau}$ under various plausible computational
complexity hypotheses.
