Might function as a decapping enzyme required for the removal of the 5'-end m7GpppN cap tethered to viral and host mRNAs to allow their decay in cells. In addition to the mRNA cap, probably also efficiently hydrolyzes diphosphoinositol polyphosphates (By similarity). diphospho-myo-inositol polyphosphate + H2O = myo-inositol polyphosphate + phosphate. Belongs to the Nudix hydrolase family. DIPP subfamily.