POPFile is an interesting, practical and very topical application of Bayesian analysis.

This simple (and free!) program is a spam filter that works with most common E-Mail programs. And very effective it is too!

It is also a very good way of appreciating and understanding how Bayesian methods work.

Once installed, POPFile takes each E-Mail you receive and decides in which of several user-defined 'buckets', it is to be placed. (These 'buckets' can then be moved automatically to say the folders in Microsoft Outlook using the features of that program.)

POPFile classifies the E-Mails using Bayesian methods on the number of times each word appears in the message and in the various 'buckets'. As it receives more and more, it refines and improves the decision making process.

Occassionally it fails to get it right!

In this case, you reassign the 'buckets' manually and POPFile learns more about the pattern of your E-Mails. Typically, POPFile removes between 98 to 99 per cent of spam!

Visit the POPFIle Web Site for more details.