General security advice

Monitor security information and vulnerability announcements from OS vendors and security analysts.

Keep your system up-to-date with all relevant security patches and software updates.

A number of cryptographic applications can protect sensitive data and prevent some kinds of spoofing and forgery.

• ssh (secure shell) provides encrypted login access with cryptographic host and user and authentication, and a scp command for encrypted file transfer
• SSL can be used to protect data for HTTP, POP and IMAP mail transfer, and some other TCP-based protocols
• PGP or GPG provide end-to-end encryption for email, and the ability to provide signed messages for authentication

Firewalling and packet filtering are good additional layers of defense, but don't depend on them as your sole security protection. They are difficult to manage and maintain, don't protect against attacks in data that you would allow through the firewall anyway (such as email or web pages), and users often find ways to bypass the aspects of the firewall they find inconvenient.

Ultimately, security increases inconvenience for users, since it makes system access and use more complicated. Users often find ways to undermine security measures that they find particularly inconvenient. It often helps to educate users about the need for security measures.

Unfortunately, the Internet is a hostile security evironment. You aren't being paranoid if they really are out to get you.