Steve Kemp's Blog Writings relating to Debian & Free Software

The problem with the English language is all those pesky words

Sunday, 29 June 2008

There exist many bayasian/statistical spam filters, ranging from products such as spambayes, and spamassassin, to crm114. Each of them works in their own way. Having used and tested almost all of them I've noticed a common flaw.

The vast majority of spam-filters struggle to correctly classify "419 scam" mails, lottery fraud, and similar mails.

Why is that? In general, having read hundreds of these mails, I can see several things that are common in these kind of the mails:

  • Mention of currency in both numeric and word forms. ($1,000,000 + 1 million US dollars)
  • Mention of a country / nationality (Sierra Lione, Nigerian)
  • Mention of a reference/claim number and often "official address".
  • Christian references.
  • Greetings such as "dear friend", and mentions of discretion/secrecy.
  • Size. (A scam mail is typically greater in length than an average spam mail).

Whilst none of these individually are indicative of a scam mail it is interesting to count their combined occurance.

I've written a toy program to count these things, and so far the success rate is >60% which is a reasonable start - providing this kind of detection occurs after normal filtering.

I may experiment further, but I figured a public query on scam detection might be appropriate.

Whilst the detecting a scam mail is a subset of detecting a spam email there are probably simplifications that may be made, and exploring those wouldn't be a bad thing.

ObQuote: Buffy.

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