...considered the king of free network IDS tools. For a free multi-platform host IDS, take a look at OSSEC. Monitoroutbound network traffic to detect infected systems that seek instructions or leak data to their masters. You can tune a...
http://searchsecurity.techtarget.com/tip/0,289483,sid14_gci1304183,00.html
...protect against inbound threats, such as viruses, worms and spam. Far fewer organizations have deployed systems that monitoroutbound content. However, the growing use of email and instant messaging, coupled with the growing variety of other communication...
http://www.findwhitepapers.com/whitepaper3092/