Microsoft has revealed that almost all e-mails sent today are spam – though the figure fell slightly with the disconnection of a hosting provider which numbered a major spam network among its customers.

The figures only relate to e-mails sent to customers of the Microsoft Forefront Online Security for Exchange service (FOSE) rather than the internet as a whole, though that’s a sample group big enough that it should be pretty representative of all web users.

In the second half of last year, 97.3% of all e-mails which went through FOSE were filtered out as spam. That figure is actually a slight drop on the first half of the year as the number of spam messages picked up by the system fell from around 80 billion to 50 billion after web hosting firm McColo had its connection cut.

Two internet service providers ditched McColo as a customer after an industry-wide investigation in conjunction with the Washington Post concluded the firm was hosting sites responsible for three-quarters of the world’s spam. It also hosted the bogus sales sites which many of the spam messages linked to.

As the Microsoft figures only go up until December, they don’t give any answer to the question of whether the spammers have been able to find new hosts and rebuild their network.

The report also shows that Microsoft’s anti-spam techniques continue to work more effectively. Until 2007, only around 60% of messages were marked as spam at the first filtering stage which looks at the origins of the message and whether it is properly addressed. Today that figure is 89.7%, meaning barely a tenth of spam makes it to the content filtering stage which looks for keywords.

There are also some cultural changes in the tactics of spammers. Microsoft broke down the subjects of spam mails for the first and second half of the year. The biggest rises were among general product advertising and pharmaceutical products, while there were sharp falls in the proportion of spams dealing with sexual performance drugs and stock tips.

The stock tips drop is likely down to the economy and a widespread lack of confidence in even ‘hot tip’ investments. The sexual performance drop (so to speak) may be misleading as there has been a large rise in the number of spams which come in the form of an image and thus the wording can’t easily be scanned.