  Ground Level Enhancements (GLEs) of cosmic-ray intensity occur, on average,
once a year. Due to their rareness, studying the solar sources of GLEs is
especially important to approach understanding their origin. The SOL2001-12-26
eruptive-flare event responsible for GLE63 seems to be challenging in some
aspects. Deficient observations limited its understanding. Analysis of extra
observations found for this event provided new results shading light on the
flare. This article addresses the observations of this flare with the Siberian
Solar Radio Telescope (SSRT). Taking advantage of its instrumental
characteristics, we analyze the detailed SSRT observations of a major
long-duration flare at 5.7 GHz without cleaning the images. The analysis
confirms that the source of GLE63 was associated with an event in active region
9742 that comprised two flares. The first flare (04:30-05:03 UT) reached a GOES
importance of about M1.6. Two microwave sources were observed, whose brightness
temperatures at 5.7 GHz exceeded 10 MK. The main flare, up to the M7.1
importance, started at 05:04 UT, and occurred in strong magnetic fields. The
observed microwave sources reached about 250 MK. They were not static. Having
appeared on the weaker-field periphery of the active region, the microwave
sources moved toward each other nearly along the magnetic neutral line,
approaching a stronger-field core of the active region, and then moved away
from the neutral line like expanding ribbons. These motions rule out an
association of the non-thermal microwave sources with a single flaring loop.
