Firewall Always On? Pros and Cons of Firewall

It would be helpful if you read this article on Wikipedia that explains the basics of firewalls. It should answer some of your questions.

If you use a hardware router connected to your cable or DSL modem, then you don't need to turn on the OS X firewall unless you feel the need for added protection. For most home installations firewalls are not necessary. No one is likely to try hacking into your computer. If you feel that insecure then turn on the firewall. Now, that said it's a somewhat different matter for wireless. If you have a wireless network and do not have security enabled in your router then your computer is at risk, and you should turn on the firewall. The following should be useful reading:

Do You Need Anti-Virus Protection for Your Mac?

According to Rich Mogull's article, Should Mac Users Run Antivirus Software?,

"The reality is that today the Mac platform is relatively safe. There are hundreds of thousands of viruses and other malicious software programs floating around for Windows, but less than 200 are known to target the Mac, and many of those are aimed at versions of the Mac OS prior to Mac OS X (and thus have no effect on a modern Mac).

It's not that Mac OS X is inherently more secure against viruses than current versions of Windows (although it was clearly more secure than Windows prior to XP SP2); the numerous vulnerabilities reported and patched in recent years are just as exploitable as their Windows equivalents. But most security experts agree that malicious software these days is driven by financial incentives, and it's far more profitable to target the most dominant platform."

Mr. Mogull is a computer security expert. I recommend reading the entire article as it is quite informative.

For additional information on viruses, trojans, and spyware visit The XLab FAQs and read the FAQs on viruses and spyware.