Typically the only thing you can do is follow the so called "Best Practices" of Internet security. Good AV, Firewall (for Inbound AND Outbound traffic, and good Anti spyware software.
Common sense goes a very long way to preventing viruses and spyware infections
And if you are really concerned about future protection of your WoW account, I would recommend investing in the Blizzard Authenticator. Handle little key fob