The "ancient virus" is a rare strain of virus found exclusively within the genes of fossilized queen ants, first discovered by Umbrella senior chief researcher Alexia Ashford. Little is known of the virus' specific function. Unlike most viruses, the ancient virus is apparently incapable of jumping species; it had no effect upon humans until it was combined with the Progenitor virus. The resultant virus was later named T-Veronica.
When infected with the T-Veronica, ants responded to Alexia's manipulation. This suggests the ancient virus may contain elements of ant DNA in its own coding. Other properties of the T-Veronica, such as combustible blood, control of a host, are likely due to the influence of the Progenitor virus.
The ancient virus is similar to the strain of t-Virus produced by James Marcus in his study of leeches. It is unknown if the viruses are biologically related.