A recent study of MessageLabs concerning the evolution of spam was published here. It gives some interesting statistics about spam during the first semester 2004:
5.0 billion emails scanned (anti-spam service), thereof 3.2 billion identified as spam, i.e. 63.5%. In comparison, during the same period in 2002, the quote represented 1.5%, in 2003 37.9%.
5.6 billion emails scanned (anti-virus service), thereof 468 million containing virus, i.e. 8.3%. In comparison, during the same period in 2002, the quote represented 0.3%, in 2003 0.5%.
MessageLabs intercepted about 1.5 million phising emails (emails containing URLs to fraudulent websites) during the same period.