Tufts University, Office of Information Technology, MAC Security Macintosh Security Don't get too smug, Macintosh computers connected to the network have security issues too. Among the SANS Institute's Ten Most Critical Security Threats are two that apply equally to Macs.
File sharing is at the top of the DON'T list.
No one can get files on your desktop unless they have physical access to it. If file sharing is turned on, the owner of the Macintosh has access to all the files on all disks on the computer, even if none of the disks have been shared. Use good passwords. San Diego and Arizona State provide detailed instructions for dealing with sharing. Unsecured Guest Access and bad passwords are still used to break into thousands of computers.