How does the UV work for destroying the bacteria, virus and other micro-organisms?

We all know sun light can be used in sterilizing, actually what functioned is Ultraviolet ray only. Ultraviolet was found about 200 years ago and through years of survey and experiment, science has proofed it's effect in killing the virus and bacteria. ultraviolet is divided by A, B, C waves and 240~260nm out of C wave is the most effect ray with sterilizing ability and the strongest point is 253.7nm. The light wave is able to kill the DNA of virus and bacteria and make it unable to reproduce.