Portable Free Apps : Use it And Enjoy it

Angry IP Scanner (or simply ipscan) is an open-source and cross-platform network scanner designed to be fast and simple to use. It scans IP addresses and ports. Angry IP scanner simply pings each IP address to check if it’s alive, then optionally it is resolving its hostname, determines the MAC address, scans ports, etc. The amount of gathered data about each host can be extended with plugins.

This is right for someone who doesn’t like other touch his PC and keep his secret. TrueCrypt is perfect.
TrueCrypt - Free open-source disk encryption software for Windows Vista/XP, Mac OS X, and Linux
Main Features:
* Creates a virtual encrypted disk within a file and mounts it as a real disk.
* Encrypts an entire partition or storage device such as USB flash drive or hard drive.
* Encrypts a partition or drive where Windows is installed (pre-boot authentication).
* Encryption is automatic, real-time (on-the-fly) and transparent.
* Provides two levels of plausible deniability, in case an adversary forces you to reveal the password:
1) Hidden volume (steganography) and hidden operating system.
2) No TrueCrypt volume can be identified (volumes cannot be distinguished from random data).
* Encryption algorithms: AES-256, Serpent, and Twofish. Mode of operation: XTS.

Using Password Safe you can organize your passwords using your own customizable references—for example, by user ID, category, web site, or location. You can choose to store all your passwords in a single encrypted master password list (an encrypted password database), or use multiple databases to further organize your passwords (work and home, for example). And with its intuitive interface you will be up and running in minutes.

If you don’t want to pay more money and keep your PC safe, you can try ClamWin. ClamWin is a Free Antivirus program for Microsoft Windows 98/Me/2000/XP/2003 and Vista.
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;
* Addin to Microsoft Outlook to remove virus-infected attachments automatically.

Simple Machine Protect is portable antivirus software for your Windows Operating System, build to remove certain variant of virus, worm, trojan and spyware from your computer. SMP was designed to be a simple, open source antivirus.