XWall is a firewall that protects your network traffic and internal system by scanning every data that tries to come inside your computer. It's recommended that you use this firewall together with an anti virus of your preference, even though it has its own built-in virus scanner. It also scans and monitors HTML and TNEF and detects suspicious messages and behavior from the internal system.
This a free to try software, it's not as powerful as other anti virus however it's really effective and it does protect your computer but is expensive.
Its compatible with a many Windows Operating Systems from Windows NT to 2003.