US (EXERPT) FROM ARTICLE BY COMPUTER SECURITY EXPERT TidBITS: Computer Security: Who's Responsible?: WEB-Blog Editor Note:see weblink for full article

Practical Precautions -- Here are five easy examples of the common-sense precautions I'm talking about:

1. Secure physical access to your computers and crucial network devices. The ultimate 'denial of service' attack may just be someone walking in, unplugging your Mac, and stealing it.
2. Assign passwords that are non-trivial and difficult to guess, without being hard to remember. Trivial passwords ('abc123', 'admin', 'test', etc.) are commonly guessed by port sniffing robots, and definitely need to be avoided. At the same time, while long sequences of random characters might seem more secure, these passwords essentially force users to write them down for handy reference. [For real-world advice on how to maintain a set of memorable and secure passwords, check out Joe Kissell's 'Take Control of Passwords in Mac OS X.' -Adam]
3. When setting up network services, don't share user accounts among users. When more than one person uses the same user account, they not only automatically have access to the same content and services, but your ability to track activity is severely limited. Should you ever need to review activity logs for some reason, there may be no way to tell one user from another.
4. Minimize the number of applications running, and use software only from trusted sources. Many potential attacks aren't launched
aunched against a single application, but rather make use of multiple applications in conjunction with one another. By eliminating unnecessary applications, and avoiding software from dubious sources, you can minimize the chance that a small flaw in one program can be turned into a big hole in your system.
5. When setting up a normal desktop Mac, a server, or your network, turn on and properly configure the firewall (which is built into Mac OS X and most modern routers). While it may take a few extra minutes, this is time well-spent, even when security isn't a primary concern. It is shocking how much malicious traffic is on the Internet. Much of this traffic is more annoying than actually dangerous for Mac users, but your first defense against email harvesting robots, virus-spread port scanners, and worse is a properly deployed firewall.