Computer viruses are the real threat of twenty first century. They can do a lot of harm - damage your computer, erase or steal your data, send spam letters, clog up networks and, of course, infect more computers spreading over Internet.

It would be hard to find anyone, who has not got any experience with these harm-makers. There were few viruses, who spread all over the world, and made heavy tolls, counted in billions dollars.

However, such a big cases are rare now. Almost every computer owner has anti-virus software installed, and these programs are getting more viceless with time.

So does this mean, that computer viruses are not so harmful, and therefore more scarce? How often they creep into your computer?