applied our association procedure to the sample of the UGS defined as follows. The number of UGSs in the 2FGL is 576, but only 410 of these $\gamma$-ray sources lie in the region of the sky available in the [[*WISE*]{}]{} Preliminary Data Release. These sources can be analyzed according to our method based on the IR [[*WISE*]{}]{} colors. We adopted a more conservative selection restricting our sample to 313 UGSs out of 410, excluding sources with a [[*Fermi*]{}]{} analysis flag, since these sources might not be real and/or could be affected by analysis artifacts [see e.g. @abdo11 for more details].

The [[*WGS*]{}]{} association method {#sec:method}
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In Paper III, working on the AGUs, we built the [[*WGS*]{}]{} parametrization to verify if the low-energy counterparts of the AGUs, associated in 2FGL, is consistent with the [[*WGS*]{}]{}, so being a $\gamma$-ray blazar candidate. With respect to the previous analysis, the following proposed association procedure aims at providing new $\gamma$-ray blazar candidates, possible counterparts of the UGSs, that lie within their $\gamma$-ray positional uncertainty regions, on the basis of our previous results on the IR-$\gamma$-ray blazar properties. In this Section, we report the basic details of our [[*WGS*]{}]{} parametrization together with the definition 