Classical methods, such as Zeeman splitting or Faraday rotation, allow to measure astrophysical magnetic fields only down to 10^-5 - 10^-7 G. Large scale intergalactic magnetic fields (IGMF) in voids can be easily 10 orders of magnitude weaker and require much more elaborated methods. Observations of the GeV and TeV gamma rays from distant active galaxies can shed some light on the existence and strenght of such fields in the Universe. In this talk we will cover the topic of the creation of gamma-ray halos by virtue of the interactions with IGMF. We will put a special attention to experimental limitations of making such measurements, and review recent findings.