Illustration of the low-level contamination leaking through the closed NIRSpec MSA, as measured from ground-based calibration data. Left: undispersed exposure through the closed MSA, clearly showing individual failed-open shutters (blue circles), as well as the low-level leakage across the MSA. Center: Enlarged subsection of the MSA showing the leakage pattern around individual shutters. Right: highly over-sampled image of the leakage pattern, obtained by superposition of the (re-binned) leakage signal from many individual shutters.