The viruses that capable of inducing cancer (tumor inducing viruses) are called as oncogenic viruses. The region of the viral genome (either DNA or RNA) that can cause tumor is called as Oncogene. The foreign gene can be carried to the cell by the virus thereby causing the cells to alter its properties.
Some of the oncogenic viruses are:
Epstein-Barr virus (EBV)
Simian Virus 40 (SV 40)