  The current response of a d-wave superconductor containing a single impurity
is calculated and shown to be singular in the low-temperature limit, leading in
the case of strong scattering to a 1/T term in the penetration depth
$\lambda(T)$ similar to that induced by Andreev surface bound states. For a
small number of such impurities, we argue this low-$T$ upturn could be
observable in cuprate superconductors.
