Just a little additional note: the most common way for a virus to travel is through email attachments (files that come with mail you get sent). The single most effective thing I have found is to block attachments entirely (you can do this with filters in your mail program). You don’t want to make a filter, just get in the habit of deleting everything that has an attachment. Don’t open it, don’t read it, just delete it. Get yourself a yahoo mail account and have your friend send attachments there instead, they get filtered and checked for viruses before you even get them!