Many Mac users find they need to use Windows too. There’s nothing wrong with that, as a large number of business applications don’t work the same or don’t exist at all for OS X.
When using Windows software on OS X, there are a couple of ways to go. You could use something like WINE (a Windows emulator) or use a virtualization tool like VMware Fusion or Parallels Desktop and a Boot Camp partition or other VM. Most of the folks I’ve met use virtualization, and that leads to a couple of issues and risks that OS X wouldn’t have natively.
First, there’s security. Running Windows in a VM and/or Boot Camp and allowing OS X applications to share data with it means that Windows virus and malware attacks can infect other software and files. While it won’t be able (in the vast majority of cases) to infect the Mac, it can still destroy data and cause havoc. It also means that accidentally opening the wrong email attachment in OS X could open the infected attachment in Windows – where it can execute and run riot. You could disable data sharing between the VM and OS X, though that means that a lot of functionality you want to use will be disabled as well.
Also, since the VM may bypass the local firewall – this depends on your VM network settings – personal information and data stored in the VM could fall victim to attacks. If the VM can see your data in OS X directories, then that data is vulnerable as well.
So, first things first, get an anti-malware tool and personal firewall for your Windows VM/Boot Camp. Microsoft makes Security Essentials available free through Windows Update, so that is a great place to start for anti-malware. Ensuring the Windows Firewall is on and active helps keep others out. Details on both of these tools can be found on the Microsoft website.
Next, make sure you update your Windows Boot Camp partition and any VM’s regularly. Too many of us use Windows very infrequently, and that means that the installations of Windows remain offline, and don’t get updated automatically like a desktop running Windows as the primary OS can be configured to do.
There are two ways to do this. You can manually run Windows Update from the Start menu at least once per month. Microsoft releases patches the first Tuesday of each month, so running Windows Update on the second full week of each month will keep you covered. Second, you can set Windows Update to automatically apply updates whenever it sees them. This isn’t the best method though, because it will mean you get hounded for reboots unexpectedly, and you do not get anything but the more critical updates installed.
No matter what, remember that if you run Windows at all, you need to keep it patched and protected. With Parallels and VMware automatically sharing documents folders, Windows malware can cause quite a bit of damage, even to OS X.