Viruses are similar to hijackers. They infiltrate normal, living cells and utilize them to proliferate and generate other viruses like themselves. This can cause you to get ill by killing, damaging, or changing your cells. Viruses assault certain cells in your body, such as those in your liver, respiratory system, or blood. These attacks can be direct, causing the cell death mentioned above, or indirect, causing the cell to malfunction or produce less vital proteins. Viruses are responsible for many common illnesses that we all know about, such as the common cold, flu, stomach virus, and hepatitis. But they can also cause more serious problems if they invade the brain or heart, for example. Virus infections can also lead to cancer. The most severe cases of AIDS are caused by viruses called HIVs. They attack certain cells in the immune system and destroy them, allowing other diseases to run their course. Cancer is when cells divide without control, which allows other cells to divide too. Viruses can cause cancer by destroying these control mechanisms so cancer cells can grow and multiply. There are three main ways that viruses can harm humans: by causing disease, by making you feel sick to make you stop moving around, and finally by killing cells. Viruses use their ability to replicate themselves to spread quickly through a population. This can lead to many people becoming infected with a virus all at once.