The DansGuardian Anti-Virus Scanner gives you the ability to virus-scan all content that passes through DansGuardian. It uses the scanning code from the MailScanner project to do the actual virus scanning, so it supports all the virus engines that the MailScanner project supports. The scanning is done as the file is being downloaded, so your current network apps don't have to be modified, etc. They just have to support using a proxy.
MailStripper Pro is a mail scanner that aims to remove spam and viruses from incoming mail. It recognises and decodes many obfuscation techniques used by spammers and uses several different mechanisms to recognise spam which are immune to Bayes poisoning, and has achieved real-world success of over 99.8%. It is MTA-independent and does not implant itself into your mail server. Instead, it functions as a proxy, allowing the MTA to reside on a different server.
P3Scan is a full transparent proxy server for email clients. It runs on a Linux box with iptables (for port redirection). It can be used to provide email scanning from the Internet to any internal network, and is ideal for helping to protect your "Other OS" LAN from harm, especially when used in conjunction with a firewall and other Internet proxy servers. It is designed to enable scanning of incoming email messages for viruses, worms, trojans, spam, and harmful attachments. Because viewing HTML email can enable a spammer to validate an email address (via Web bugs), it can also provide HTML stripping.
smtpfilter is a filter for an SMTP session which passes the session through transparently in real time, except for the DATA command which is intercepted in order to scan the data for spam and/or viruses with the scanner of your choice. The sources are heavily commented. The default spam filtering is a hybrid approach that uses spamassassin to self-train the excellent spamprobe Bayesian filter which works on a per-site rather than per-user basis. The virus checking can use clamav or NAI, or any other command- line scanner.
Etherpuppet is a small program for Linux that will create a virtual interface (TUN/TAP) on one machine from the ethernet interface of another machine through a TCP connection. Everything seen by the real interface will be seen by the virtual one. Everything sent to the virtual interface will be emitted by the real one. It has been designed because one often has a small machine as his Internet gateway, and sometimes want to run some big applications that need raw access to this interface, for sniffing (Ethereal, etc.) or for crafting packets that do not survive being reassembled, NATed, etc. It can even run on Linux embedded routers such as the Linksys WRT54G.
SafeSquid is a content filtering proxy server. It supports 'profiled' Internet access, a browser based interface, very fast throughput, DNS caching, content caching, pre-fetching, bandwidth control, virus scanning, ICP, CARP, and ICAP clients, source, target, and time-based granular firewall style rules to allow or deny content like music, videos, Flash and Java applets, messengers, chats, cookies, ActiveX, scripts, etc., remote authentication, real-time text and image analysis for blocking pornography, and an URL filter.
Tor is a network of virtual tunnels that allows people and groups to improve their privacy and security on the Internet. It also enables software developers to create new communication tools with built-in privacy features. It provides the foundation for a range of applications that allow organizations and individuals to share information over public networks without compromising their privacy. Individuals can use it to keep remote Websites from tracking them and their family members. They can also use it to connect to resources such as news sites or instant messaging services that are blocked by their local Internet service providers (ISPs).