The invention relates to antiviral agents and specifically to synthetic biologically-active derivatives, and can be used in the pharmaceutical industry, in medicine, in plant husbandry and in biotechnology. The antiviral agent is based on poly-N1-hydrazino(imino)methyl-1, 6-hexanediamine-poly-N1-amino(imino)methyl-1, 6-hexane diamine of general formula (1), where : HX is an acid, n=3-20, and m=4-20, and which is active against viruses of humans, animals, plants, bacteria and fungi, said viruses being non-enveloped and enveloped and containing RNA or DNA. The antiviral agent exhibits a broad range of effectiveness, and is active against viruses both in intracellular and extracellular locations.