From my experience, there is no anti virus program that can protect your computer perfectly. Today's viruses are disabling anti viruses itself. I'm not saying that you should not use an anti virus. I highly recommend you use one, let it be free or paid. You are not done yet! The anti virus program must be updated to deliver the best protection. And I see, still viruses can get away from these anti viruses. Check this list to find if your computer is infected Common symptoms: Unknown entries in the start up list of Windows Executable files getting created when you run programs (This can also happen in removable medias) Files/folders in removable media disappears Programs functioning weird (failing to start/crashing/hanging up) You see multiple processes of the programs in task manager (eg. When you run Mozilla Firefox, you see more than one instance of firefox.exe in task manager's processes list) Random programs using your internet connection Virus affected