  We report about a short flare from the blazar NRAO 530 occurred on 17
February 2004 and detected serendipitously by the IBIS/ISGRI detector on board
INTEGRAL. In the 20-40 keV energy range, the source, that is otherwise below
the detection limit, is detected at a level of ~2 x 10^-10 erg cm^-2 s^-1
during a time interval of less than 2000 s, which is about a factor 2 above the
detection threshold. At other wavelengths, only nearly-simultaneous radio data
are available (1 observation at 2 cm on 11 February 2004), indicating a
moderate increase of the polarization. This appears to be the shortest time
variability episode ever detected in a high luminosity blazar at hard X-rays,
unless the blazar is contaminated by the presence of an unknown unresolved
rapidly varying source.
