Open Source Alternative to Commercial Software - Security and Privacy

CommView

Wireshark is the world's foremost network protocol analyzer, and is the standard in many industries.

Kaspersky Anti-Virus Personal, Symantec Norton AntiVirus

ClamWin is a Free Antivirus program for Microsoft Windows 98/Me/2000/XP and 2003.ClamWin Free Antivirus comes with an easy installer and open source code. You may download and use it absolutely free of charge. It features: high detection rates for viruses and spyware; scanning Scheduler; automatic downloads of regularly updated Virus Database; standalone virus scanner and right-click menu integration to Microsoft Windows Explorer;
Clam AntiVirus is an open source (GPL) anti-virus toolkit for UNIX, designed especially for e-mail scanning on mail gateways. It provides a number of utilities including a flexible and scalable multi-threaded daemon, a command line scanner and advanced tool for automatic database updates. The core of the package is an anti-virus engine available in a form of shared library.
Winpooch is a Windows watchdog, free and open source. Anti spyware and anti trojan, it gives a full protection against local or external attacks by scanning the activity of programs in real time. Associated with ClamWin antivirus, Winpooch keeps safe your computer against virus. Winpooch uses the API Hooking method. It spies programs when they are running and gives to the user a powerful control of their activity.For example, you can forbide a program to write in a system directory or in the registry, or else to connect to internet. That makes the difference between others anti spywares using a database of known signatures.

Lavasoft Ad-Aware SE
Winpooch is a Windows watchdog, free and open source. Anti spyware and anti trojan, it gives a full protection against local or external attacks by scanning the activity of programs in real time.
Spybot Search & Destroy is great for removing spyware and other malware.
Windows Defender is the Microsoft free anti-spyware program which when used in conjunction with another spyware scanning software can improve spyware removal chances.
PGP Desktop

GnuPG is the GNU project's complete and free implementation of the OpenPGP standard as defined by RFC2440 . GnuPG allows to encrypt and sign your data and communication, features a versatile key managment system as well as access modules for all kind of public key directories. GnuPG, also known as GPG, is a command line tool with features for easy integration with other applications. A wealth of frontend applications and libraries are available. Version 2 of GnuPG also provides support for S/MIME.
Email Cryption (Thunderbird)
Enigmail is an add-on you can utilize for encrypting email once you've installed PGP.
PGP Whole Disk Encryption
TrueCrypt is free open-source disk encryption software for Windows Vista/XP/2000 and Linux. Main Features: creates a virtual encrypted disk within a file and mounts it as a real disk, encrypts an entire hard disk partition or a storage device such as USB flash drive. Encryption is automatic, real-time (on-the-fly) and transparent.
FreeOTFE is a free, open source, "on-the-fly" transparent disk encryption program for PCs and PDAs. Using this software, you can create one or more "virtual disks" on your PC/PDA. These disks operate exactly like a normal disk, with the exception that anything written to one of them is transparently, and securely, encrypted before being stored on your computer's hard drive.

Sunbelt iHateSpam
Mozilla’s Thunderbird email application features many new enhancements to help you better manage your unruly inbox, and stay informed.
The Anti-Spam SMTP Proxy (ASSP) Server project aims to create an open source platform-independent SMTP Proxy server which implements whitelists, Bayesian, and basic anti-virus filtering to rid the planet of the blight of unsolicited email (UCE).