General
The most important aspect of maintaining the security of your Mac is to ensure that you are regularly updating your machine. The updates should be automatic, and you can always verify that you're up to date by going to the Apple icon and choosing Software Update.
Apple has a Best Practices document that may be of interest as well. It is located here
iTunes
iTunes has the ability to share your library, and see other shared libraries. In our environment this may not be something that you would like to have happen. This is relatively simple to turn off and the following series of screenshots should show you how.
First open iTunes Preferences by choosing iTunes and then Preferences from the titlebar. A window like this should appear.
You will note that "Share my library on my local network" is unchecked. If yours is checked, you may wish to uncheck it.
Finder Sharing
OSX has the ability to share files and folders. If you incautiously configure sharing, you may allow your files to be accessed by anyone who can see your machine on the network.
The default options when you share a file or directory add an extra user to the permissions: "Everyone" is allowed read-only access. This is something you most certainly do not want under normal circumstances.
In this example I've shared a folder called "Share" that I intend to mount from another Mac in my office. I do not want the files on Share to be accessable by anyone but myself. I have opened the Folder Info and you'll see the "Sharing and Permissions" at the bottom.
If you click the lock in the lower right corner and enter your password you will be able to modify the permissions of the Share folder. You want to change the permissions on "Everyone" to "No Access" as shown below.
This technique works on any item you may wish to share, from a single file to an entire disk. Be sure to verify your permissions before creating a share and you should be OK.
