Anti Virus software is your computers immune system. It is a program that runs on your computer checking it for virus activity. Anti virus software needs regular updating to keep up with the latest virus doing the rounds. Anti Virus vendors usually incorporate 'update contracts' with their software, so that users can keep up with the latest anti virus solutions on an ongoing basis. Those whose computers have a lot of contact with others systems, need to ensure they are well protected. Even adopting simple preventative measures such as not opening e-mail attachments sent from unknown sources, can be a big help.