Anti-virus software does remove viruses, but you can be more proactive with you protection. Yes, Norton, Mcafee, 
PCCillin, AVG and others provide automated protection to computers, but they are reactionary in removing viruses after the viruses are found.
You can be more proactive by performing the following:
-Do not open suspicious attachments.
-Do not open e-mails from unknown senders.
-Do not click on links in e-mails from unknown senders.
-Permanently delete suspect e-mails by holding down the SHIFT key and hitting DELETE.
Purchasing anti-virus software is necessary as is being cautiously smart about your e-mail usage. The majority of viruses are spread through viruses. So please be careful when checking your e-mails.