As mentioned while looking at spam filtering in previous blogs, botnets

(networks of ‘bots’) are being noted as an increasing source of

cyber-criminal activity. A securityfocus article

( quotes shocking figures

from The Messaging Anti-Abuse Working Group; as many as 7% of PC’s

worldwide are infected and working as active bots, that’s around 47

million. They also estimate that bots now send 70% of all spam–this is

an increasing problem for System Administrators as it means many more

residential broadband IP addresses are being blacklisted by projects

like SpamHaus. I have had several instances where users trying to send

mail from outside of the corporate network have been unable to due to

being in a dns blacklist (while not infected themselves, a previous user

of the dynamic IP address must have been).