A mutagenic retrovirus was a type of biogenic weapon, comprised of genetically engineered viruses. When used on a population, mutagenic retroviruses could cause millions of casualties in a short period of time.
In 2373, the Regent of Palamar purchased a quantity of mutagenic retrovirus from Hagath and Gaila's arms business for use against General Nassuc's homeworld. However, Quark, unwilling to have the deaths of 28 million people on his conscience, told them that their supplier had sold all his stock to the Minnobia for their war against the Vek. (DS9: "Business as Usual")