Heparin has been known to be a broad-spectrum inhibitor of viral infection for almost 70 years, and it has been used as a medication for almost 90 years due to its anticoagulant effect. This nontoxic biocompatible polymer efficiently binds to many types of viruses and prevents their attachment to cell membranes. However, the anticoagulant properties are limiting their use as an antiviral drug. Many heparin-like compounds have been developed throughout the years; however, the reversible nature of the virus inhibition mechanism has prevented their translation to the clinics. In vivo, such a mechanism requires the unrealistic maintenance of the concentration above the binding constant. Recently, we have shown that the addition of long hydrophobic linkers to heparin-like compounds renders the interaction irreversible while maintaining the low-toxicity and broad-spectrum activity. To date, such hydrophobic linkers have been used to create heparin-like gold nanopartides and beta-cydodextrins. The former achieves a nanomolar inhibition concentration on a non-biodegradable scaffold. The latter, on a fully biodegradable scaffold, shows only a micromolar inhibition concentration. Here, we report that the addition of hydrophobic linkers to a new type of multifunctional scaffold (dendritic polyglycerol, dPG) creates biocompatible compounds endowed with nanomolar activity. Furthermore, we present an in-depth analysis of the molecular design rules needed to achieve irreversible virus inhibition. The most active compound (dPG-5) showed nanomolar activity against herpes simplex virus 2 (HSV-2) and respiratory syncytial virus (RSV), giving a proof-of-principle for broad-spectrum while keeping low-toxicity. In addition, we demonstrate that the virucidal activity leads to the release of viral DNA upon the interaction between the virus and our polyanionic dendritic polymers. We believe that this paper will be a stepping stone toward the design of a new dass of irreversible nontoxic broad-spectrum antivirals.