The infrared detectors of the ISO instruments are very sensitive to impacts by high energy particles and gamma rays. Each such impact produces a spike in the pixel or detector output, which can severely degrade the quality of a photometric measurement or -- in the worst case -- ruin parts of a source spectrum.
In-orbit performance shows that the impact rate is higher than expected pre-launch. This has led to revisions in instrument commanding and observing strategy as well as to software routines in data reduction. Details can be found in the addenda to the OBSERVER'S MANUALS and the ISO Data User's Manuals.