There's already a fair bit of work into engineering a virus to kill cancer. This research is about getting that virus to also induce an immune response to kill other cells that have been recruited to support the cancer in the body.
The clever trick is that these viruses are programmed to target cancer by engineering them to not be able to survive in non-cancer cells. In the case of ColoAd1, the virus will be destroyed by the p53 found in normal cells, but missing from cancer cells.
Engineered viruses might also be evolved or engineered specifically with a kill switch mechanism or be selected to be highly sensitive to a particular antiviral medication.
The current literature is bleak on the subject of controlling nature.