Viruses cause all types of infections and diseases. Some of the most common viral infections are the common cold, the flu, and warts. Some of the more severe diseases that viruses cause are HIV/AIDS, smallpox, and hemorrhagic fevers like Ebola and Marburg. In order for viruses to cause an infection, they must take their genetic material and hijack normal, living cells to produce more viruses with the same genetic material. Since viruses live inside cells of the body, they are hard to kill. But there are vaccines that can protect humans from many viral infections. Learn more about various viral infections and vaccines.