For me, it depends on what you're planning to use your Laptop for.
If you're into heavy multimedia production stuff, better get the mac, but I'm not saying that Mac can't be used for the office setting, it's also an excellent choice for the office setting but I think you'd get more if you'd use it for multimedia. But, for me, one of the main advantage of having the Mac is that you'd get the best of both world. You can install Windows in it via bootcamp.
If, you'd like to play a lot of games on your laptop, get a Dell XPS, or if you're really heavily dependent on Windows-Based Apps.
When it comes to viruses, it's a myth that Macs are virus free or virus proof, it's just that people who make viruses don't see Mac as a big enough target.
Security wise, i'd say both are very vulnerable.