Viruses in nature are micro-organisms that can only survive in another living cell. The DNA is the life program or life architecture that is written into the cell to ensure correct functioning, reproduction and growth. Different viruses attack different kinds of cells, and so they have different effects on the body, causing different illnesses. In our bodies our immune system recognizes these intruders as foreign and attacks them in order to render them harmless. It takes the evil into itself as it were.
Computer viruses are minute programs that latch onto another program and then copy themselves.
There are many types and not all of them are very destructive, but ones like the Melissa virus or the time bomb I mentioned earlier re-write themselves all over the parts of the hard disc where the operating system is kept. This is like destroying parts of the DNA of a cell so that the original life program is lost. These programs are written by computer hackers who get a kick out of being able to exert power. Their behaviour stems out of the human ability to twist what is good. Instead of using God's gift of intelligence to create they use it to destroy.