The Technical term warm or hot pixel describes a CCD characteristic that can be observed when long exposure times are used (generally >3s, although this can vary from chip to chip). If images are recorded using these long exposure times, it is observed that single pixels seem to be much brighter than their surrounding area. If dark images (closed optical input) are recorded using long exposure times, it is observed that at the same locations, bright pixels can be seen.
These bright pixels are called warm or hot pixels. Physically, the false information comes from charge leakages within the CCD image sensor chip. Although the warm pixels are randomly distributed within the chip, they are in a fixed position. Under normal conditions (shorter exposure times, normal light), they are not visible because their contribution to the general noise level is below this level.