Viruses are known only for harmful effects and are not useful. They cause various diseases like polio,rabies,chicken pox,mumps etc
What Are Some Harmful Effects Of Viruses?
They can harm your health...
They r the worst.....
If you mean human viruses the effects can sometimes be devistating. They can cripple and even kill. The virsus in machinces can do prtty much the sam thing to them