Skill Level 3: Expert Cracker
1) Require authentication to access any network resource
2) Segment your network
In the extreme case, a computer not attached to a network is safe from network-based intrusion. But there are other ways to keep network users away from where they shouldn’t be. A few properly-connected Inexpensive NAT-based routers can be used to establish firewalled LAN segments while still allowing Internet access. See this How To for the details.
3) Bulk up your software-based protection
At minimum, you need to run current versions of good anti-virus applications that automatically update their virus definition files. Personal firewalls such as ZoneAlarm can alert you to suspicious use of your network. And, unfortunately, the latest generaton of malware and spyware threats make adding an anti-spyware application also necessary. Webroot Software’s Spy Sweeper seems to be getting good marks lately, along with Sunbelt Software’s CounterSpy.
4) Encrypt your files
Encrypting your files with strong encryption should provide effective protection in the event unauthorized users do gain access to them. Windows XP users can use Windows Encrypted File System (EFS). Mac OS X users can use FileVault. The downside to encryption is that it takes time and computing power to encrypt and de-crypt files, which could slow things down more than you’d like.