It's nothing out of the ordinary. A Mac really is just a PC... It's a UNIX, so it runs most of the same daemons, servers, and CLI tools that Linux and BSD do. The only different between Macs and PCs is the operating system, especially now that they use x86.
It still can't be affected by any kind of trojan or virus, but there will always be holes in software and servers that can be exploited.
Since it is a UNIX, a proper set up from the start from a security standpoint would eliminate most of the severity problems. At most, a hacker could probably gain access to that specific user's content, but not anything else. You could probably lock that down further by eliminating which applications you use.
Besides, it's not like Internet Explorer or Mozilla Firefox ever had any exploits before.
