  We present new, simultaneous, multifrequency observations of 45 out of the 55
candidate High Frequency Peakers (HFP) selected by Dallacasa et al. (2000),
carried out 3 to 4 years after a first set of observations. Our sub-sample
consists of 10 galaxies, 28 stellar objects (``quasars'') and 7 unidentified
sources. Both sets of observations are sensitive enough to allow the detection
of variability at the 10% level or lower. While galaxies do not show
significant variability, most quasars do. Seven of them no longer show the
convex spectrum which is the defining property of Gigahertz Peaked Spectrum
(GPS)/HFP sources and are interpreted as blazars caught by Dallacasa et al.
(2000) during a flare, when a highly self-absorbed component dominated the
emission. In general, the variability properties (amplitude, timescales,
correlation between peak luminosity and peak frequency of the flaring
component) of the quasar sub-sample resemble those of blazars. We thus conclude
that most HFP candidates identified with quasars may well be flaring blazars.
