AGB stars are not expected to host coronae or chromospheric activity capable to produce X-ray emission, yet there is a growing population of AGB stars that present X-ray emission, the so-called X-AGB stars. This X-ray emission most certainly arises from an accretion disk around a companion fed by the copious stellar wind of the AGB. In some cases the companion would be a white dwarf in a binary symbiotic star system. The brightness of the AGB star outshines the system, making unfeasible the detection of the spectral features used to diagnose symbiotic stars. Here I will present the observations supporting the evidence for a hidden population of symbiotic stars with an AGB component (or a hidden population of AGB stars in binary systems).