One of the most effective desktop Bayesian filters available is SpamBayes, shown in Figure 4-4. SpamBayes is an Outlook plug-in that monitors incoming e-mail and applies Bayesian filtering before it arrives in your inbox. It's extremely easy to configure, and very effective at filtering spam.

Figure 4-4: SpamBayes configuration.

To begin using SpamBayes, simply download the Outlook add-in and follow the installation wizard. You're asked to supply two sets of e-mails: one set of spam and one set of ham. If you don't have enough spam to train SpamBayes at the moment, simply skip the configuration and wait a few days until enough has built up in your inbox. You can then restart the training process by opening the SpamBayes manager from the toolbar icon, selecting the Training tab, and then clicking Start. Figure 4-5 shows SpamBayes processing the selected spam and ham folders:

Figure 4-5: SpamBayes training.

You'll find that within a week of training SpamBayes, the spam you receive will be cut down dramatically.

One extremely interesting feature of SpamBayes is the ability to see the clues used to detect whether a message is spam or ham. When you select an e-mail (either spam or ham), and then select Show spam clues for current message from the SpamBayes menu, SpamBayes generates a statistical summary for you, similar to the one shown in Figure 4-6:

Figure 4-6: SpamBayes statistical analysis.

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It can be very interesting to see exactly which words and phrases trigger the Bayesian filter!

Network Bayesian Filtering

If you have more than one computer that downloads e-mail, you might find it practical to use a different type of filtering system. Because the Outlook Junk E-mail filter and SpamBayes are client-side filtering systems, they can only protect the computer on which they're installed. To provide more comprehensive spam filtering from a single computer, inline spam firewalls are used. Spam firewalls such as No Spam Today are similar to a proxy server in that they sit between your ISP's e-mail server and your home network, scanning all incoming e-mail regardless of which computer it's destined for.

One of the best programs in this genre was SpamAssassin; however, McAffee has commercially discontinued the product and absorbed its functionality into a different suite.

Inline spam firewalls are favored by large organizations for a number of reasons. First, they're easier to manage than individual desktop filters -- although users lose the individual control over their spam filtering, from a corporate point of view, the overall result is far more effective. Second, once an organization is sufficiently large, the licensing costs for desktop applications become enormous. It's far more economical to spend $2,000 on one spam firewall than to buy 1,000 desktop licenses at $5 or $10 each. The more popular corporate spam firewalls include the Barracuda and GFI Mail Essentials.

Moving On

Congratulations on completing this course! Over the last four lessons you've learned a lot of technical information and practical steps about how to stay safe on the Internet. Spyware and spam are serious issues, but they can be managed with the right knowledge and tools.

The learning process never ends, and there's always something new to investigate! This course has given you a solid knowledge foundation in the world of spyware and spam, as well as the tools to protect yourself. Although the threats and issues may slowly change in future, the basic principles won't.

Make sure you do the assignment and take the quiz for this lesson; they cover elements from all four lessons and will help fill in any gaps. Finally, don't forget to stop by the Message Board to discuss spyware, spam, and security issues with your instructor and fellow students.