Internet Security Software in Linux
The most powerful, readily available tool for internet security is the firewall. Firewalls contain a set of rules telling a computer what Internet connections to accept and which to reject. There are a number of different firewall programs available in Debian, most of them usable on other operating systems as well. Technically, these are frontends to the iptables functionality built in to the Linux kernel. One such frontend is Firewall Builder (or fwbuilder for short), and you can check out an fwbuilder tutorial.
Antivirus programs are typically not needed in Linux as they are in Windows, because there aren’t as many vulnerabilities and they are fixed faster. Open source software is generally more secure than its closed source relatives, because there are so many people working on the code and it is available to all. Problems are fixed much faster. Also, Linux handles files differently from Windows, making it less vulnerable to viruses. However, there are antivirus programs available, though they are typically closed-source; Panda Antivirus is one.
Open Source Internet Security Software in Windows
Even if you aren’t running Linux on your computer, there is open source internet security software available. Clamwin is an open source security scanner that scans for viruses and spyware. It has integration into the system and a Microsoft Outlook addon to help protect you from email viruses and trojans. Installing (and using) programs such as the Firefox web browser instead of Internet Explorer and Thunderbird instead of Microsoft Outlook can make you safer. They are open source and have features to help you get the most security you can, including many addons to protect you from phishing and many common attacks.
Secure Your Browser
Remember, the biggest thing you can always do to protect yourself from threats online is to be careful: don’t click on things unless you’re reasonably certain you know what they are, and don’t click “yes” unless you know what you’re agreeing to! Mozilla offers tips to keep yourself safe online.