Is your computer running slower than it should be? Do you often get mysterious error messages? Are you not able to run certain programs? If so, then there is a chance that your computer is infected by a virus. This is one of the major problem faced by almost all users across the globe. There are many kinds of viruses, worms and trojan that may infect and harm your computer. Some are harmless, but, they do have the capacity to do any number of nasty things including erasing all data from your computer and multiplying its own copies. However there are many ways by which you can keep these viruses and worms away from your PC. Here are 12 ways to maintain a virus free computer.