  We investigate the performance of two machine learning algorithms in the
context of anti-spam filtering. The increasing volume of unsolicited bulk
e-mail (spam) has generated a need for reliable anti-spam filters. Filters of
this type have so far been based mostly on keyword patterns that are
constructed by hand and perform poorly. The Naive Bayesian classifier has
recently been suggested as an effective method to construct automatically
anti-spam filters with superior performance. We investigate thoroughly the
performance of the Naive Bayesian filter on a publicly available corpus,
contributing towards standard benchmarks. At the same time, we compare the
performance of the Naive Bayesian filter to an alternative memory-based
learning approach, after introducing suitable cost-sensitive evaluation
measures. Both methods achieve very accurate spam filtering, outperforming
clearly the keyword-based filter of a widely used e-mail reader.
