We present the mid-infrared colors of X-ray-detected AGN and explore mid-infrared selection criteria .
Using a statistical matching technique , the likelihood ratio , over 900 IRAC counterparts were identified with a new MUSYC X-ray source catalog that includes \sim 1000 published X-ray sources in the Chandra Deep Field-South and Extended Chandra Deep Field-South .
Most X-ray-selected AGN have IRAC spectral shapes consistent with power-law slopes , f _ { \nu } \propto \nu ^ { \alpha } , and display a wide range of colors , -2 \leq \alpha \leq 2 .
Although X-ray sources typically fit to redder ( more negative \alpha ) power-laws than non-X-ray detected galaxies , more than 50 % do have flat or blue ( galaxy-like ) spectral shapes in the observed 3-8 \mu m band .
Only a quarter of the X-ray selected AGN detected at 24 \mu m are well fit by featureless red power laws in the observed 3.6-24 \mu m , likely the subset of our sample whose infrared spectra are dominated by emission from the central AGN region .
Most IRAC color-selection criteria fail to identify the majority of X-ray-selected AGN , finding only the more luminous AGN , the majority of which have broad emission lines .
In deep surveys , these color-selection criteria select 10-20 % of the entire galaxy population and miss many moderate luminosity AGN .